The shooting in the western town of Qusair also wounded many others, according to several Syrian human rights and activists groups.

Anti-government protests are common in Qusair and, combined with the early morning assault on the town of Saraqeb near the Turkish border, reflected the determination of President Bashar Assad to crush the five-month old uprising despite mounting international condemnation.

US President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan agreed during a phone call Thursday on the need for a "transition to democracy" in Syria, the White House said.

Obama's office said he and Erdogan also had agreed on the need for an "immediate halt of all bloodshed and violence against the Syrian people" by forces loyal to Assad.

The US imposed new sanctions Wednesday, and a flurry of foreign diplomats have rolled through Damascus urging Assad to end a campaign of killing that rights groups say has left about 1,700 dead since mid-March.

A US-based international human rights groups released a report accusing Syrian authorities of targeting medical facilities, health workers and their patients. It called on the government to safeguard doctors' obligations to provide neutral and ethical care for civilians.

Physicians for Human Rights said security forces control access to hospitals, and many injured civilians in need of critical care are forgoing treatment because they fear being detained and tortured if they seek care at government-controlled medical facilities.

"In addition to the widely reported atrocities committed by the government, PHR has received reports of serious violations of medical neutrality in Syria," a statement by the group said.

It also quoted a group of Syrian physicians as saying 134 doctors have either been detained by the government or have disappeared.

The attack on Saraqeb is particularly noteworthy because it sits in Idlib, a province bordering Turkey.

Tanks, troop carriers and buses transporting security force members sped into the town after dawn Thursday, Syrian Observatory for Human Rights reported.

"Shooting was heard soon afterward," it said, adding that security forces were "raiding homes and making arrests, rounding up more than 100 people, including 35 children."

"Army troops are smashing the doors of shops owned by activists in search of them, and they have cut off electricity in the town," where anti-regime protests have been held nightly, said the Observatory.

The military said this week it withdrew from Hama in central Syria, following a weeklong military siege operations in the defiant city. A group of Turkish journalists who toured Hama for four hours Thursday saw two APCs parked at the main square keeping watch over the city center and soldiers on some streets, but no tanks or heavy weaponry in sight.

"The soldiers and security forces destroyed everything, they didn't leave anything. We are in God's hands," one man they spoke to said, speaking on condition of anonymity for fear of reprisal.