Gunfire reverberated in the streets and dead bodies still lay on the pavements on Tuesday in the southern Syrian city at the heart of the uprising against President Bashar Assad, residents said, in a sign that the regime’s brutal crackdown continued unabated.

Also Tuesday, a Syrian human rights group said authorities detained dozens across the country, mainly in several Damascus suburbs and in the northern coastal city of Jableh.

The developments came a day after the Syrian Army, backed by tanks and snipers, launched a deadly raid on Daraa, where the uprising in Syria started over a month ago. Monday’s pre-dawn raid left at least 11 dead in the southern city.

The head of the Syrian Observatory for Human Rights, Rami Abdul-Rahman, couldn’t provide a precise figure for those arrested in Tuesday’s sweeps. He said the group had little news about Daraa since it was difficult to get through after authorities cut mobile telephone service in the city.

A Daraa resident told The Associated Press on Tuesday “dead bodies were still in the streets because no one has been able to remove them.”

“We are being subjected to a massacre,” the man screamed over the telephone as cracks of gunfire reverberated in the background. “Children are being killed. We have been without electricity for three days, we have no water.”

The man, who spoke over a Jordanian mobile phone, said Syrian special forces were in the streets of the city. He added that Daraa, an impoverished city near the border with Jordan, was bombed by tanks.

A relentless crackdown since mid-March has killed more than 350 people across Syria, with 120 alone dying over the weekend, rights groups said. But that has only emboldened protesters who started their revolt — inspired by uprisings in the Arab world — with calls for modest reforms but are now increasingly demanding Assad’s downfall.

The witness spoke on condition of anonymity for fear of reprisals.

Syria has banned nearly all foreign media and restricted access to trouble spots since the uprising began, making it almost impossible to verify the dramatic events shaking one of the most authoritarian, anti-Western regimes in the Arab world.

Daraa, a drought-parched region of 300,000 in the south, has seen some of the worst bloodshed over the past five weeks as the uprising gained momentum. Recently, the city has absorbed many rural migrants who can no longer farm after years of drought.

The uprising was touched off by the arrest of teenagers who scrawled anti-government graffiti on a wall.

The attack on Daraa was by far the biggest in scope and firepower. Video purportedly shot by activists showed tanks rolling through streets and grassy fields with soldiers on foot jogging behind them.

State-run television quoted a military source as saying army units entered the city to bring security “answering the pleas for help by residents of Daraa.”

As the Syrian government stepped up its crackdown, the U.S. State Department urged Americans to defer all travel to Syria and advised those already in the country to leave while commercial transportation is still available. It also ordered some nonessential U.S. embassy staff and the families of all embassy personnel to leave Syria. It said the embassy would remain open for limited services.

Syria has a pivotal role in most of the flashpoint issues of West Asia — from the Arab-Israeli peace process to Iran’s widening influence. Instability has thrown into disarray the U.S. push for engagement with Damascus, part of Washington’s hopes to peel the country away from Hamas, Hezbollah and Tehran.

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