Hundreds of Syrians have fled to Turkey after elite Syrian troops moved to encircle the restive town of Jisr al-Shughour ahead of a possible assault, sharply escalating the upheaval that threatens the 40-year regime led by President Bashar Assad.
There were widespread reports that the government had lost control of much of the northern province of Idlib, as well as unconfirmed accounts of some residents fighting back with weapons.
In Geneva, UN high commissioner for human rights Navi Pillay accused Syria of trying to "bludgeon its population into submission" by attacking anti-government protesters with snipers, tanks and artillery.
Elite fourth division troops believed to be led by Assad's younger brother Maher had almost surrounded Jisr al-Shughour, leaving open one route to the border, according to activist Mustafa Osso.
The town lies 12 miles from Turkey, which has prepared camps for an influx of refugees. About 1,800 Syrians have fled into Turkey since the start of the 11-week nationwide uprising against Assad, which has been marked by weekly protests of thousands and a deadly crackdown.
"The reinforcements are complete and the army could storm the city at any moment," Mr Osso said after talking to contacts in the area.
The struggle over Jisr al-Shughour is a critical test for Assad's government, which said "armed groups" had killed 120 security forces in the area but has not commented on reports of a mutiny by some military units opposing the crackdown.
Al-Watan, a pro-government newspaper, reported on Thursday that the army was mobilising large forces and bracing for a confrontation that would last days. It said troops faced an estimated 2,000 gunmen backed by many young men from local villages.
The Syrian government, which sharply restricts local media and expelled foreign journalists, has blamed recent violence on gunmen and religious militants. Activists say more than 1,300 people, most of them civilian protesters, have died in the uprising.
Al-Watan newspaper also said residents in Idlib were evacuating homes "to give the Syrian army a chance to enter all areas and confront the gunmen".