BEIRUT, Lebanon - The death toll from Syria's crackdown on a nine-month-old uprising has exceeded 5,000 people, the top U.N. rights official said Monday, as Syrians closed their businesses and kept children home from school as part of a general strike to pressure President Bashar al-Assad to end the bloodshed.

Navi Pillay, the U.N. high commissioner for human rights, said that those killed in the Assad regime's attempts to stamp out the revolt include at least 300 children, and that thousands of people remain in detention.

Speaking at the United Nations, Pillay said she told Security Council members of the increase in deaths and recommended that the council refer Syria to the International Criminal Court for investigation of possible crimes against humanity.

Susan Rice, the U.S. ambassador to the United Nations, urged the council to take concrete steps to bring the violence to an end.

Assad has shown little or no sign of easing his crackdown, despite mounting international pressure, including a recent spate of economic sanctions from the European Union, the Arab League, and Turkey that are punishing the Syrian economy - a dangerous development for the government in Damascus.

Now, the open-ended strike by Syrian businesses also takes direct aim at Syria's already ailing economy. It is designed to erode Assad's main base of support: the new and vibrant merchant classes that have benefited in recent years as he opened up the economy.

If the economy continues to collapse, the authoritarian president could find himself with few allies inside Syria, where calls are growing by the day for him to step down.

It is difficult to gauge the strength of the strike because the regime has banned most foreign journalists and prevented local reporters from moving freely. But there were signs it was being widely observed in particular in centers of antigovernment protest: the southern province of Daraa, the suburbs of the capital of Damascus, the northwestern region of Idlib, and the restive city of Homs.

The opposition wants the strike to remain in force until the regime pulls the army out of cities and releases thousands of detainees.

"Only bakeries, pharmacies, and some vegetable shops are open," said one Homs resident who asked that his name not be published for fear of reprisals. He said those stores stayed open because they sell essential goods.

He said security was tight in Homs, with agents at every intersection. The crackle of gunfire erupted sporadically. "There is a terrifying security deployment in Homs," he said.

Activists said new clashes between Syrian troops and army defectors began Sunday with a major battle in the south and spread Monday, raising fears the conflict is spiraling toward civil war.

At least 16 people were reported killed nationwide Monday, mostly in Homs, according to various activist networks.

The uprising has grown increasingly violent in recent months as defecting soldiers fight back against the army and once-peaceful protesters take up arms to protect themselves.

Amid the violence, the government pushed ahead with municipal elections that the opposition has dismissed as a meaningless concession. Witnesses said turnout was low.