BEIRUT – The death toll in the Syrian uprising has soared to at least 3,500 people, the United Nations said Tuesday, a sobering measure of the scope of a military crackdown that has bloodied city after city but failed to crush the 8-month-old revolt against President Bashar Assad’s regime.

Under the strain of daily killings, some Syrians see a dangerous fracturing of society as long-festering resentments over religion, sectarian identity and poverty bubble to the surface. Moreover, there were new signs that the protesters, who so far have been largely unarmed, are increasingly starting to fight back, threatening to increase the bloodshed.

The dangers have been on display this week in the country’s third-largest city, Homs. Security forces are besieging the city for the third time this year to stamp out the epicenter of the revolt.

Most notably this time, dissident troops have been putting up a stiff defense as security forces blast their way into rebellious neighborhoods. Amid the fighting, there have been tit-for-tat sectarian killings suspected to be between Sunni Muslims, who largely back the protests, and Alawites, a Shiite sect that makes up the backbone of Assad’s regime.

In Geneva, a spokeswoman for the U.N. High Commissioner for Human Rights said the count of 3,500 dead throughout the uprising was likely a conservative figure.

“We are deeply concerned about the situation and by the government’s failure to take heed of international and regional calls for an end to the bloodshed,” said Ravina Shamdasani.

She told The Associated Press the new death toll comes from a variety of credible sources both within and outside Syria. The information is then corroborated by the U.N. human rights office.

Though internationally isolated, Assad appears to have a firm grip on power with the loyalty of most of the armed forces, which in the past months have moved from city to city to put down uprisings. In each place, however, protests have resumed.

In Homs, one of Syria’s most diverse cities with a population of about 1 million people, security forces have been assaulting Sunni-majority districts, raiding homes and fighting dissident troops — particularly in the neighborhood of Baba Amr.

Electricity, water and phone lines have been cut to the restive neighborhood, where a man and a woman were killed by security forces’ gunfire on Tuesday, according to activist Salim al-Homsi.

“There are mountains of garbage everywhere,” al-Homsi said. “It is difficult to bring in medical equipment, bread and heating fuel. There is a shortage of everything.”