Thousands of Syrian soldiers encircled the northern border town of Jisr al-Shughour in a bid to roust anti-government rebels who have been calling for President Bashar Assad to step down since late March, the BBC reported.
The government said the assault was in retaliation for the deaths of about 120 security personnel in the town his week, although various reports alleged the men were killed by the army for plotting a mutiny, the British broadcaster said.
Meanwhile, Turkish Foreign Ministry official Halit Cevik told the broadcaster at least 4,300 Syrians had officially crossed the border to escape the fighting, although a BBC correspondent said many more had migrated without documentation.
The United States is urging the Syrian government to allow the Red Cross access to the area.
"Syrian leaders have no excuse for denying humanitarian assistance by a neutral body like the ICRC [International Committee of the Red Cross]," Obama administration press secretary Jay Carney said in a statement. "If Syria's leaders fail to provide this access, they will once again be showing contempt for the dignity of the Syrian people."
Cevik said Turkey hadn't yet sought assistance from the United Nations High Commissioner for Refugees, as most of the Syrians are expected to return home whenever the violence ends.
Turkey has established tent cities for the Syrians and Cevik said the country would "do whatever is needed within our means."