Syrian troops have launched a broad ground assault on rebel-held areas of the besieged city of Aleppo.
The official SANA news agency claimed regime forces had fully regained control on Salaheddine - the main rebel stronghold in the northern city. It said the military inflicted heavy losses upon "armed terrorist groups," the government's catch-all term for its opponents.
But Rami Abdul-Rahman, the director of the Britain-based Syrian Observatory for Human Rights, said troops met resistance in the offensive.
President Bashar Assad's regime has suffered a series of setbacks over the past month that point to mounting chaos in the country after a 17-month-uprising that has morphed into civil war. Four senior security officials were assassinated in Damascus, there have been a string of high-level defections including the prime minister this week, and government forces have struggled to put down rebel challenges in Damascus and Aleppo.
The regime has far more powerful weapons than the rebels and still has a firm grip on much of the country.
Aleppo, the largest city in Syria and its commercial centre, holds great symbolic and strategic importance. Around 25 miles from the Turkish border, it has been a pillar of regime support during the uprising. An opposition victory there would allow easier access for weapons and fighters from Turkey, where many rebels are based.
There has been a marked increase in the number of refugees fleeing to Turkey in the past two days as Aleppo-based activists reported fresh clashes. Intense government bombardment of the Syrian town of Tal Rafaat closer to the border also sent scores of people spilling into Turkey for safety, the activists said.
Some 2,400 people crossed into Turkey overnight to escape the escalating violence.
Assad has been forced to rely on a shrinking list of allies, including Iran. Senior Iranian envoy Saeed Jalili visited Damascus on Tuesday, appearing with Assad in a show of solidarity.
The rebels have blasted Iran's influence in the country and over the weekend, rebel forces intercepted a bus carrying 48 Iranians and kidnapped them. Rebels claimed the men are military personnel, including some members of Iran's powerful Revolutionary Guard, who were on a "reconnaissance mission" to help Assad's crackdown on the uprising.