Monday's crackdown came a day after Syrian opposition groups met in Istanbul and urged international action to stop what they called indiscriminate killings of civilians by the authorities.
The United States welcomed the development, saying it was encouraged by the opposition's statements supporting non-violence, and blamed the mounting death toll on the Syrian authorities.
Local activists said a military operation on Monday focused on Talbiseh near Homs, 150 km (94 miles) north of Damascus, after security forces entered the nearby town of Rastan, which lies on the highway between the capital and the northern city of Aleppo.
For about a week, tank- and helicopter-backed troops have battled insurgents and army deserters in Rastan, in the most sustained fighting since Syria's uprising began in March. The official Syrian news agency said on Saturday government forces had regained control of the town.
"Tank fire targeted Talbiseh this morning and communications remain cut. The town was key in supplying Rastan and now it is being punished for that," one activist said. "House to house arrests are continuing in the area for the second day."
Armed insurgents, mostly in the central Homs region and the north western province of Idlib, have been so far outgunned.
Activists said dozens of villagers had been arrested in Talbiseh in the past 48 hours and there were deaths and casualties from the raids.
Information also was scarce from Rastan, which has been sealed off since tanks moved in at the weekend. Activists said hundreds of people were believed to have been arrested and held in schools and factories in the town.
Events on the ground are difficult to verify as the authorities have expelled independent journalists from the country or banned them from working, although some foreign reporters have been allowed to visit.
Amnesty International said that Syrian diplomats in foreign capitals are mounting campaigns of harassment and threats against expatriate dissidents protesting outside their embassies.
Syrian opposition supporters have mounted noisy protests outside many embassies in recent months as the government of Bashar al-Assad has tried to put down unrest with what observers say has been a bloody crackdown.
Amnesty said on Tuesday that embassy officials had filmed and threatened some of those involved in protests outside Syria, and that in some cases relatives in Syria had been deliberately targeted for harassment, detention, torture and outright disappearance.
"Expatriate Syrians have been trying, through peaceful protest, to highlight abuses that we consider amount to crimes against humanity - and that presents a threat to the Syrian regime," said Neil Sammonds, Amnesty International's Syria researcher.
Syrian officials have generally denied reports of human rights abuses, with the Assad government saying it has no choice but to restore law and order and avert chaos.
While some Assad opponents have taken up arms, others are still staging demonstrations against his 11-year rule. Night protests erupted on Sunday in several districts of Homs, where a crowd in the Khalidiya district shouted, "Homs is free."
A surge in sectarian killings has heightened tensions in the city. The state news agency said "armed terrorist groups" killed five people there on Monday. Residents said two bodies had turned up in the city's Sunni Qarabid neighbourhood.
Homs has a mixed population, with a few Alawite neighbourhoods inhabited by members of Assad's minority sect, alongside others populated by majority Sunni Muslims.
Underlining the turn towards violence, the authorities said Sariya Hassoun, the son of Mufti Ahmad Hassoun, Syria's state-appointed top cleric, was assassinated in Idlib on Sunday.
It was the first attack on the state-backed Sunni clergy who have backed Assad for decades, despite widespread Sunni resentment at Alawite dominance.
Assad, 46, who succeeded his father in 2000, blames the violence on foreign-backed armed gangs. His officials say 700 police and soldiers have died, as well as 700 "mutineers".
As Syria's struggle has grown bloodier, claiming at least 2,700 lives so far, according to a UN count, demonstrators have begun to demand some form of international protection that stops short of Libya-style Western military intervention.
A statement issued in Istanbul on Sunday by a newly formed opposition National Council rejected intervention that "compromises Syria's sovereignty", but said the outside world had a humanitarian obligation to protect the Syrian people.
"The Council demands that international governments and organisations meet their responsibility to support the Syrian people, protect them and stop the crimes and gross human rights violations being committed by the current illegitimate regime."
The council said the uprising must remain peaceful but that military assaults, torture and mass arrests were driving Syria "to the edge of civil war and inviting foreign interference".
It also said the Muslim Brotherhood, the Damascus Declaration -- which groups established opposition figures -- and grassroots activists had all joined the Council.