Turkey has scrambled two fighter jets after a Syrian military helicopter bombed the Syrian border town of Azmarin.
The town has been the site of fierce fighting between rebels and government forces .
Rebels battled to hold onto Syria's main north-south highway as government forces fought insurgents on several fronts across the country.
On the Turkish-Syrian border, tensions between Ankara and Damascus are worsening at a time when the 19-month-old conflict is intensifying, with no sign of a diplomatic breakthrough and growing concerns that the violence could spread across the Middle East.
The pro-opposition Syrian Observatory for Human Rights gave a death toll for Thursday of more than 260 people, including civilians and combatants on both sides, as fighting raged in the capital and the north, west and east of the country.
It said 92 soldiers had been killed on Thursday, one of the highest daily tolls on the government side since the uprising against President Bashar al-Assad broke out in March 2011.
The official SANA news agency also reported fighting nationwide and said dozens of rebels, which it called "mercenary terrorists", had been killed.
In Idlib, activists said opposition fighters captured about 400 soldiers and loyalist militiamen this week in Western Jisr al-Shoughour, a hilly agricultural area.
Photos released by the opposition showed dozens of uniformed soldiers sitting on the ground in what appeared to be a hangar.
"Around 400 loyalist troops have been captured. Many of them were poor conscripts who were let go. The more important officers are being interrogated," a rebel source said.
The British-based Observatory, which has a network of monitors in Syria, reported fighting at a military barracks close to Maarat al-Nuaman, a town on the highway from Homs to Aleppo in the northwest.
Assad's forces also ramped up air strikes and artillery barrages against Homs after they took heavy losses trying to overrun the rebel-held Khalidiya district. "There are 50 bodies of soldiers and shabbiha (militia) on the streets in Khalidiya and regime troops cannot retrieve them," said Ahmad Tarkawi, a local opposition leader.