BEIRUT — Syrian troops going house to house have detained more than 3,000 people in the past three days in the rebellious town of Rastan, which saw some of the worst fighting of the 6-month-old uprising recently, activists said Monday.

Over the past week, the military fought hundreds of army defectors who sided with anti-regime protesters in Rastan. The fighting demonstrated the increasingly militarized nature of the uprising and heightened fears that Syria may be sliding toward civil war.

The activist group Local Coordination Committees said fighting in the town has now stopped after the military operation that left dozens dead. The group and a Rastan-based activist confirmed about 3,000 in the town of 70,000 had been detained. The activist told The Associated Press that detainees are being held at a cement factory, some schools and a massive four-story compound.

“Ten of my relatives have been detained,” said the activist, who asked that he be identified only by his first name Hassan for fear of retaliation. He said he was speaking from hiding in Rastan.

Syria’s opposition movement has until now focused on peaceful demonstrations, although recently there have been reports of protesters taking up arms to defend themselves against military attacks. Army defectors have also been fighting government troops, particularly in Rastan, the town just north of Homs that government forces retook on Saturday.

The fears of civil war, possibly along sectarian lines, were also heightened by the assassination Sunday of the 21-year-old son of Syria’s top Sunni Muslim cleric — the latest in a string of targeted killings.

The state-appointed cleric, Grand Mufti Ahmad Badreddine Hassoun, who is considered a loyal supporter of President Bashar Assad’s regime, accused the opposition of creating the climate for his son’s killing and blamed rival, anti-Assad Sunni clerics for allegedly issuing fatwas, or religious edicts, inciting against him.

“My brothers who were misguided and carried arms, you should have assassinated me because some clerics issued such fatwas. Why did you kill a young man who did nothing and harmed no one?” Hassoun, holding back tears, said in a sermon at his son’s funeral, aired on Syrian TV stations.

The killing was the latest in a series of targeted executions of prominent people including a nuclear engineer, university professors and physicians. The men, a mixture of Alawites, Christians and Shiites, were all killed in a hail of bullets in the past week.

The regime has accused “terrorist gunmen” of the killings, while the opposition in turn accused the regime of trying to foment sectarian strife to maintain its grip on power.

Syria’s volatile sectarian divide means that an armed conflict could rapidly escalate in scale and brutality. The Assad regime is dominated by the Alawite minority, an offshoot of Shiite Islam, but the country is overwhelmingly Sunni Muslim. Alawite dominance has bred resentments, which Assad has worked to tamp down by pushing a strictly secular identity for the state.

He has exploited fears of a civil war fears by portraying himself as the only power who can keep the peace.

Meanwhile, Russia and China vetoed a U.N. Security Council resolution Tuesday that threatened sanctions aganst Syria if it didn’t immediately halt its military crackdown against civilians.

European members of the Security Council tried to avoid a veto by watering down the language on sanctions three times, but they failed.

The vote was 9-2 with four abstentions — India, South Africa, Brazil and Lebanon.

The Security Council has been divided over a response to the violence, with Western nations and some supporters in Africa and Latin America pressing for tough action against Syria while Russia, China and other members opposed even mentioning the threat of sanctions.

In a sign that Assad’s regime might be reaching beyond Syria’s borders in its crackdown, Amnesty International said in a report released Monday that Syrian expatriates in eight countries, including many in the United States, have been systematically monitored and harassed by embassy officials and others believed to be acting on behalf of the government.

In some cases, relatives back home have been detained, beaten and harassed to silence relatives who are protesting overseas. Some families in Syria appear to have been forced to publicly disown their relatives abroad.

The AP has reported on recent attacks that appear to be part of a fearsome new tactic of retaliating against protesters’ families to snuff out the uprising, including the beheading of 18-year-old Zainab al-Hosni to pressure her activist brother to turn himself in and an attack on the parents of Syrian pianist Malek Jandali.

The uprising began in mid-March amid a wave of anti-government protests in the Arab world that have so far toppled autocrats in Tunisia, Egypt and Libya. Assad has reacted with deadly force that the U.N. estimates has left some 2,700 people dead.

Printed October 5, 2011 as: Syrian troops arrest 3,000 in three days