Rebels battled to hold onto Syria's main northeastern highway on Friday as government forces fought insurgents on several fronts across the country.
The rebels captured an air defence base east of Syria's biggest city, Aleppo, and government forces unleashed air strikes and artillery bombardments on the western city of Homs, activists said.
On the Turkish-Syrian border, Turkey scrambled two fighter jets after a Syrian military helicopter bombed the Syrian border town of Azmarin.
The incident was the latest sign that tension between Ankara and Damascus is surging at a time when the 19-month-old conflict is deepening with no sign of a diplomatic breakthrough and growing concerns that it 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, in violence 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.
The reports could not be independently verified but they indicate an intensifying conflict, with the daily body counts of the past several weeks far exceeding previous months.
The British-based Observatory, which has a network of monitors in Syria, said fighting was taking place at a military barracks close to Maarat al-Nuaman, a town on the highway from Homs to Aleppo in the northwest.
Aleppo, Syria's commercial hub, has been contested since July and the rebel capture of Maarat al-Nuaman this week cut the main route for Mr. al-Assad's military to resupply and reinforce it.
Opposition sources said rebels on Thursday halted an armoured army column at Khan Sheikhoun which had been sent from Hama to retake Maarat al-Nuaman, 70 kilometres south of Aleppo. They also reported artillery barrages along the highway between Khan Sheikhoun and Maarat in the past 72 hours.
SANA said government forces were trying to clear Aleppo's Karm al-Jabal area of rebels on Friday.
More than 30,000 people have been killed in the conflict, which started out as a popular uprising against four decades of Assad family rule and domination by their Alawite sect and then spiralled into civil war.
Fighting has also spilled over its borders into Turkey, Lebanon, Jordan and the Israeli-occupied Golan Heights, stoking fears that the war could drag in its neighbours.
Since Syrian bombardments hit Turkish villages last week, Ankara and Damascus have squared off militarily and rhetorically, with Turkey moving troops up to the border and threatening to retaliate if there is further cross-border bloodshed.
Turkey infuriated Syria on Wednesday when it forced a passenger plane flying from Russia to Syria to land in Ankara. The Turkish authorities said it was carrying Russian-made munitions for the Syrian army, a charge denied by Damascus and Moscow.
Turkey allows rebels sanctuary on its soil and has led calls, along with Western powers and Gulf Arab states, for Mr. al-Assad to step down. The Syrian president counts on the support of Russia and Iran.
Despite the bluster, most analysts believe that neither Syria nor Turkey want matters to get out of hand. The United States and European powers have also shown no desire to intervene militarily, despite much hand-wringing over the bloodshed.
Mr. al-Assad's forces also intensified air strikes and artillery barrages against Homs on Friday, a day after they took heavy losses trying to overrun the rebel-held Khalidiya district, opposition activists said.
"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.
"The situation remains tough. The regime is now using a multiple rings tactic to surround Homs."
Homs, 140 kilometres north of Damascus, was the focus of world attention in February when a government siege pulverized rebel-held districts and killed hundreds of fighters and civilians. It is also a gateway to the mountains overlooking the Mediterranean, heartland of Mr. al-Assad's minority Alawite sect.
Video footage showed a six-storey building in Khalidiya flattened by an airstrike.
Shelling and aerial bombardments were also hitting Sunni Muslim towns near Homs to prevent rebels in the countryside from joining the battle for Homs, opposition activist Abu Yazan said.
Meanwhile, the refugee crisis grew ever more acute, with the UN refugee agency UNHCR saying that between 2,000 and 3,000 people were fleeing across borders every day from Syria.
The total number of refugees now stood at more than 340,000, Melissa Fleming, a UNHCR spokeswoman, said in Geneva.
"And now into the winter months, more and more of these people are going to be living in camp situations. So more and more of these people are going to be spending the winter in tents," she said.