The Syrian army shot dead at least five people in a town near the Lebanese border and stormed another town near Turkey's border, activists said.
The shooting in the town of Qusair also wounded 16 people, according to the Syrian Observatory for Human Rights.
But Damascus-based Abdul-Karim Rihawi, head of the Syrian Human Rights League, said seven people were killed.
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.
The US imposed new sanctions on Wednesday.
Foreign diplomats have urged Assad to end a campaign of killing that rights groups say has left about 1,700 dead since mid-March. Turkey's foreign minister, a day after meeting with Assad, renewed his condemnation of the attacks.
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.
Intense protests in the area triggered a harsh government response, forcing hundreds of Syrians to flee across the border. The military said it withdrew from residential districts in the area and returned to its barracks.
Troops detained at least 100 people in Saraqeb, according to the London-based Syrian Observatory for Human Rights.
Explosions and gunfire reverberated through the area after the army rolled in, said the Local Co-ordination Committees, an activist group that helps organise and document the protests.
The government justified its attacks on various cities by saying it was dealing with terrorist gangs and criminals who were fomenting unrest.
The uprising was inspired by the revolutions and calls for reform sweeping the Arab world, and activists and rights groups say most of those killed have been unarmed civilians.
International condemnation over the crackdown has been strong, and growing more forceful.
In Turkey, Foreign Minister Ahmet Davutoglu renewed calls today for an end to the bloodshed and said Turkey would be closely watching developments there.
The Obama administration, which announced new sanctions, is preparing for the first time to explicitly call for Assad to step down, officials have told the AP.