Syrian forces launched an all-out assault with troops and tanks, driving rebels from a Damascus neighborhood on Friday, according to the Associated Press.
Citing activists, the AP said over 300 people were killed in a single day.
The government assault comes just a day after news that rebels had seized the crossings to Iraq and Turkey's borders, Agence France Presse noted.
Syrian state television said, "Our brave army forces have completely cleansed the area of Midan in Damascus of the remaining mercenary terrorists and have re-established security."
Reuters reported that Syrian forces had pushed the fighters out of the central district of Midan and into southern neighborhoods, where heavy shelling and clashes were reported.
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The BBC reported that pictures from Midan showed dust-covered corpses and burnt-out cars and tanks.
According to AFP, rebel fighters also clashed with troops in several neighborhoods of Aleppo.
Reuters said the rebels are comprised of the Free Syrian Army, Al Qaeda style Jihadists, the Muslim Brotherhood and pro-democracy Sunni liberals. They are calling their offensive "Damascus Volcano and Syrian Earthquake," and both the rebels and the Syrian government seem to be referring to this as the last battle.
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Meanwhile, thousands of refugees have fled Damascus, crossing into neighboring Lebanon, according to the United Nations refugee agency, said The New York Times. A spokeswoman for the UN, Melissa Fleming, said between 8,500 and 30,000 Syrians have crossed into Lebanon in just the last 48 hours.
More than 112,000 Syrians have already registered as refugees in Lebanon, Turkey, Iraq and Jordan, according to The Times.
The UN Security Council agreed to extend its observer mission in Syria for a "final" 30 days on Friday, the BBC reported.