Syrian government forces have massed 170 tanks north of the city of Aleppo, close to the Turkish border, according to the rebel Free Syrian Army.
The claim by Gen Mustafa al-Sheikh, head of the FSA's military council, could not be independently confirmed, but it suggested that the Syrian army was responding to a Turkish military build-up on the border.
It could represent a significant escalation in tensions between Damascus its former friendly neighbour. The Syrian army has been involved in operations against rebels in the area
Meanwhile, international envoy Kofi Annan said he believed that Saturday's international crisis meeting in Geneva will end with "an acceptable result" and said he was optimistic, despite the fact that Russia, publicly at least, says it will not countenance regime change unless it comes from the Syrian people themselves.
In what could prove a crucial meeting, Hillary Clinton, the US Secretary of State, and Sergei Lavrov, the Russian foreign minister, meet in St Petersburg today to try to produce with a compromise.
The Americans are adamant that the Russians agree to a new plan drawn up by Mr Annan that would include Assad supporters in a national unity government but require him to the Syrian president to step down.
Mr Assad ruled out any compromise. In a rare interview, he said he had a duty to "annihilate terrorists" to protect his people and ruled out any solution to the crisis imposed from outside the country.
"The responsibility of the Syrian government is to protect all of our residents. You have a responsibility to annihilate terrorists in any corner of the country," Mr Assad told Iranian state television.
"When you eliminate a terrorist, it's possible that you are saving the lives of tens, hundreds, or even thousands," he said, referring to last month's massacre in the village of Houla in which more than 100 people, including women and children, were killed.
Battling to crush a 16-month uprising against his rule, the 46-year-old Alawite leader demanded international observers speak out more about the "terrorist operations" they witnessed.
He also firmly rejected any solution imposed from outside the country, emphasising his own commitment to reform instead.
"We will not accept any non-Syrian, non-national model, whether it comes from big countries or friendly countries. No one knows how to solve Syria's problems as well as we do," he said.
"We are moving forward with political reforms. But for terrorists and the governments that support them, reforms have no meaning."
Mr Assad accused Syria's foes of trying to interfere in his country's internal affairs with UN resolutions and by bringing about the failure of Kofi Annan's peace plan.