(CNN) — After 16 months of bloodshed, the Syrian cities of Aleppo and Damascus bore the brunt of conflict Sunday between rebels and President Bashar al-Assad’s regime.
Arab League diplomats, meanwhile, met in Qatar to find ways to end violence and forge peace in Syria, a country engulfed by a fierce government offensive against dissidents and an armed uprising against the regime.
In a video posted online Sunday, the head of the rebel Free Syrian Army in Aleppo announced an operation “to liberate the city of Aleppo from the rule of the Assad thugs, whose hands were blood-stained by heinous crimes against our people.”
Brig. Gen. Abdel Jabbar Al-Obeidi urged regime soldiers to defect or step aside and not fight against his men, with the promise that no one would be harmed.
Late Sunday, Syrian state television broadcast an “important” statement from the Information Ministry saying Western intelligence and “some Arab parties” are planning to hijack Syrian TV frequencies and deliver false news reports of a coup, defections, or cities having fallen into rebel hands.
State TV said the stations “might use Syrian journalists under pressure after being kidnapped.”
Fierce clashes erupted Sunday between regime and rebel forces in Aleppo, the commercial hub of Syria, opposition activists said.
“An entire building collapsed in Seif al-Dawla neighborhood after a regime tank … targeted it with four shells,” the Local Coordination Committees of Syria (LCC) said.
Syrian state-run TV cited an official media source as denying reports about Aleppo.
“Some terrorists are mobilizing their armed groups in the city in a similar attempt to distort the reality and the facts on the ground just like they tried to do in Damascus,” the network said.
“Our heroic armed forces and the special authorities in Aleppo … have been tracking down the remnants of the terrorists, killing a large number of them.” Others surrendered, while still more fled toward Turkey, according to the report.
By the end of the day Sunday, 71 people had died across Syria, including 24 people in and around Damascus and two in Aleppo, the LCC said.
If rebels eventually gain control of Aleppo, it would mark a pivotal point in the Syrian crisis and deal a heavy blow to al-Assad’s financial ties.
Separately, rebels said Sunday they had seized a border gate between Syria and Turkey at Bab al Salam.
“There were attempts to take over the border crossing of Bab al Salam for the last three days,” Malik Kurdi, deputy commander of the Free Syrian Army, told CNN. “Yesterday, very late at night, FSA seized the gate completely, and now Syrian helicopters are flying around.”
He said there are concerns Syrian forces could attack the gate.
Another FSA fighter, identifying himself as Abu Shawki, said the rebels gained control of all of Bab al Salam following fierce clashes in which many died. He said regime forces abandoned some of their tanks.
Aleppo and the capital city of Damascus have been al-Assad strongholds, but heavy clashes in Damascus over the past week, along with a recent bombing that killed four members of al-Assad’s inner circle and government, suggest cracks in the regime’s armor.
A mosque in Damascus came under attack Sunday from rocket and helicopter shelling while worshippers were inside, the LCC said. The mosque caught fire and “many” were killed, the group said.
But the Syrian regime denied reports of helicopter attacks in Damascus, saying it was “life as usual” in most of the city, Syrian state-run TV reported Sunday.
CNN cannot independently confirm reports of violence because the government restricts access by foreign journalists.
Alex Thomson, a correspondent with CNN affiliate ITN, wrote Sunday on Twitter that a military hospital in Damascus came under heavy fire, and a sustained firefight took place as rebels apparently attacked the building for about 90 minutes. The bodies of soldiers were at the hospital, he said; their funerals were canceled because of the hospital attack.
Thomson noted in a blog post he could not say for sure that rebels attacked the hospital, but soldiers at the hospital insisted it was under attack.
Separately, another opposition group reported that a senior scientist and expert in Syria’s missile program was killed, along with his wife and son.
Retired Maj. Gen. Nabil Zugheib was assassinated in the Bab Touma district of Damascus, the Syrian Observatory for Human Rights said. There was no immediate claim of responsibility.
Damascus is largely isolated by checkpoints and tanks, witnesses said Saturday. Opposition groups say medicine is running out and residents are appealing for help.
The crisis started in March 2011, when a fierce government crackdown against protesters morphed into a nationwide uprising against the regime.
The United Nations estimates more than 10,000 people have been killed since the crisis began more than 16 months ago. But Rupert Colville, a spokesman for the office of the U.N. high commissioner for human rights, said the United Nations has not been giving out overall death toll numbers since December “because it became impossible to verify the numbers in any meaningful way.”
Opposition groups tracking deaths have issued higher tolls. The LCC, for example, estimates more than 16,000 people, mostly civilians, have died.
The Syrian regime has taken a hit with military defections. An official from the Turkish Foreign Ministry said three brigadier generals from Syria arrived in Turkey last week and about two dozen Syrian generals have fled to Turkey.
CNN’s Yousuf Basil, Holly Yan, Saad Abedine, Roba Alhenawi, Ivan Watson, Raja Razek, Yesim Comert and journalist Shiyar Sayed Mohamad contributed to this report.
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