- Battles for critical ground intensify; rebel victories could "cripple" the government
- The rebel army details how it helped a high-ranking Syrian official to defect
- Video: The Syrian military has carried out "massacres" against civilians demanding freedom
- State-run media: Military is ready to "continue its crackdown on the remnants of terrorists"
(CNN) -- In what could be one of the highest-level defections from the Syrian government, the country's military police chief has reportedly left Bashar al-Assad's forces to join "the people's revolution."
In a video posted online this week, a man identified as Maj. Gen. Abdul Aziz Jassim al-Shallal announced his defection and said he was joining the country's popular uprising.
"The Syrian military has strayed from its core mission in protecting the homeland to become nothing but armed gangs that kill and destroy the cities and the villages, carrying out massacres against our innocent civilian population that came out demanding freedom and dignity," he said.
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Al-Shallal had been plotting his escape to Turkey for weeks with the help of rebels, said Louai Miqdad, a spokesman for the rebel Free Syrian Army.
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A man walks near a missile on Tuesday, December 25, at an army barracks outside Damascus, Syria, that has been taken over by the Free Syrian Army. Click through to view images from Syria from December, or see photos of the conflict from November.
Free Syrian Army fighters prepare a homemade missile before they launch it toward the military airport in Aleppo, Syria, on Sunday, December 23.
Free Syrian Army members display shrapnel from what they say are the remains of a rocket fired from the Syrian army in northern Aleppo on Thursday, December 20.
An unexploded bomb is seen lodged in a street in Ghouta, east of Damascus, Syria, Wednesday, December 19.
A Free Syrian Army fighter aims his weapon through a hole in the wall of the structure where he is positioned in the Qastal Harami area of Aleppo on December 19.
A child sits in the back of a vehicle at the border crossing leading to Masnaa, Lebanon, as people wait to stamp their documents before leaving Syria on December 19. Click through to view images from Syria from December, or see photos of the conflict from November.
Palestinian children who fled the Syrian refugee camp of Yarmuk wait at the Masnaa Border Crossing leading into Lebanon on December 19.
Syrians line up outside a bakery offering cheap bread in Aleppo, Syria on Sunday, December 16.
A Syrian boy walks past a rebel fighter in the northern town of Darkush, Syria, on Friday, December 14.
Two men on a motorcycle lead a horse through the northern town of Darkush, Syria, on December 14, 2012.
Rebel fighters push out a boat carrying two Syrian women fleeing to Turkey through the Orontes River near the northern Syrian town of Darkush on December 14.
Passengers gather at a terminal at the airport in Aleppo, Syria, on Wednesday, December 12.
A member of the Syrian opposition's Al-Buraq Brigade stands guard on a main road in the northern Syrian town of Ain Dakna near the Turkish border on Monday, December 10. Click through to view images of the fighting from December, or see photos of the conflict from November.
A Free Syrian Army fighter takes position as he aims his weapon in Aleppo's al-Amereya district on Tuesday, December 11.
Men warm themselves by a fire on a street corner in Aleppo, Syria, on Sunday, December 9.
A rebel soldier watches Al-Jazeera news in a shop near the front lines in Aleppo on December 9.
A rebel soldier prays in a shop in Aleppo on December 9.
Syrians mourn a fallen fighter at a rebel base in the al-Fardos area of Aleppo on Saturday, December 8.
A Syria rebel commander sits behind a desk in his bombed-out position in Aleppo on December 8.
A Syrian rebel fighter emerges from a hole in a wall in Aleppo on December 8.
Rebel fighters take part in a demonstration against the Syrian regime after Friday prayers in Aleppo on December 7.
A wounded rebel fighter is transported to a hospital in the back of a truck in Aleppo, Syria, on Thursday, December 6. At least 23 people died in Syria on Thursday, most of them in Damascus and Aleppo, according to the opposition Local Coordination Committees of Syria.
Rebel soldiers stand guard inside a building in Aleppo on December 6.
Angelina Jolie, special envoy for the U.N. refugee agency, meets with Syrian refugees at the Zaatari refugee camp outside Mafraq, Jordan, on December 6.
In this handout from the Shaam News Network, Free Syrian Army fighters stand guard against forces loyal to Syrian President Bashar al-Assad in the Al-khalidiya neighborhood of Homs on Tuesday, December 4.
In this handout from the Shaam News Network, Free Syrian Army fighters take cover in destroyed buildings during clashes with regime forces on December 4.
Syrians cross the border from Ras al-Ain, Syria, to the Turkish border town of Ceylanpinar on Tuesday, December 4.
Boys walk through a damaged area In Aleppo, Syria, seen through a destroyed car on December 4.
A man inspects rubble in a neighborhood of Aleppo on Sunday, December 2.
The bodies of three children reportedly killed in a mortar shell attack are laid out for relatives to identify at a makeshift hospital in Aleppo on December 2.
Smoke rises from fighting in the Hanano and Bustan al-Basha districts of Aleppo on Saturday, December 1.
Syrian-Kurdish women and members of the Popular Protection Units, an armed opposition group to the Syrian government, stand guard during a comrade's funeral in a northern Syrian border village on December 1.
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"The last three hours of al-Shallal fleeing the borders were on a scooter. This is how hard things can get when it comes to the coordination of the defections of some of the Syrian officers and how the FSA works hard to guarantee their safety and the passageway of their families," Miqdad said from Turkey.
CNN cannot independently verify many claims from Syria, as the government and severely restricted international journalists' access.
But if the military police chief did defect, it would be only the latest in a rash of high-profile defections from al-Assad's government.
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Manaf Tlass, a brigadier general and a former close friend of al-Assad's, left Syria's Republican Guard in July.
Prime Minister Riyad Hijab has also defected.
And at just one military base outside Aleppo, about 250 soldiers have defected since the Syrian uprising began last year. Most of them have joined the opposition.
The defections, combined with recent gains by rebels in various battlegrounds across the country, suggest that al-Assad is losing his grip on a country that his family has firmly commanded for more than 40 years.
But the president has given no indication that he will step down.
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On Wednesday, Syrian state-run media said military forces were confronting "terrorist groups" that "attacked safe villages" in Hama province. The government frequently describes rebels as terrorists.
The Syrian Arab News Agency also said the military was ready "to confront the aggression and continue its crackdown on the remnants of terrorists until ridding the homeland of their evils."
But Miqdad, the rebel spokesman, said it's in the best interest of Syrian officials to follow al-Shallal's lead.
"We would like to warn everyone who is serving in the Assad military: This is it. The time is near, and the FSA and the Syrian revolution are shifting the balance of power. If they don't defect now and denounce the regime, they will be considered to be traitors and they will have to face trial for the crimes that their troops committed against our people," he said.
"We urge them to defect now and join the revolution, or it will be too late."
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On the ground: Fierce battles for critical areas under way
Months of intense fighting over the city of Maaret al-Numan and the Wadi al-Deif military base came to a head Wednesday, with rebels making an elevated push for control of key government areas, dissidents said.
"If the rebels manage to take over the Wadi al-Deif base and Maaret al-Numan, it could be a severe blow to the regime in the north because it will give the rebels the upper hand in controlling the entire Aleppo-Damascus highway," said Rami Abdulrahman, director of the opposition Syrian Observatory for Human Rights.
He said such victories would be a major strategic gain because rebels would be able to cut off all the reinforcements to regime forces in Syria's largest city and commercial hub, Aleppo.
"Wadi al-Deif is considered to be the main fuel storage for the regime forces and the largest military base in Idlib province. If the rebels managed to cut off the road by taking over the base and the security checkpoints that surround it, the opposition fighters would cripple the regime forces' ability to mobilize their forces not only in Idlib, but in Aleppo as well," Abdulrahman said. "Hundreds of regime forces will be left in disarray to fight on their own without any reinforcement, fuel or food supplies."
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By late Wednesday morning, rebels had announced "the start of the liberation" of Maaret al-Numan, the opposition Local Coordination Committees of Syria said.
But the Syrian Observatory said clashes continued in the city, punctuated by heavy shelling by regime forces. Dissidents also said rebels destroyed five armored vehicles and a tank.
Across the country, about 40,000 people -- mostly civilians -- have been killed in the Syrian crisis since March 2011, according to tallies by opposition activists.
At least 38 people have been killed in Syria on Wednesday, the LCC said. Of those, 21 have died in Raqqa province.
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CNN's Holly Yan contributed to this report.