By BASSEM MROUE
BEIRUT (AP) — Gunfire and explosions erupted Thursday in the city at the heart of Syria's anti-government uprising as soldiers launched a massive crackdown, witnesses said. Terrified residents cowered inside their homes and used mosque loudspeakers to call for blood donations to help the wounded.
Details about the siege in Homs were sketchy, as most witnesses told The Associated Press they were too scared even to look out their windows. The city has seen some of the most intense violence as the regime tries to stamp out a revolt that has lasted more than four months.

"I can see smoke billowing from the neighborhood," a witness told The Associated Press by telephone from the Bab Sbaa area of Homs, about 100 miles (160 kilometers) from Damascus. Heavy gunfire crackled in the background. "We cannot leave our homes."
Calls for blood donations blared from mosque loudspeakers, raising fears of mass casualties. But the gunfire was too intense for people to collect any victims.

As darkness fell, another resident said the violence had tapered off, with only intermittent cracks of gunfire. He said Syrian soldiers in personnel carriers were leaving the area.
Both spoke on condition of anonymity for fear of reprisals by the government.
The regime has banned nearly all foreign media and restricted coverage, making it nearly impossible to independently verify events on the ground or casualty figures.

Activists say up to 50 people have been killed in Homs since Saturday, a wave of violence that has signaled a potentially dangerous turn in the uprising. According to witnesses and activists, much of the bloodshed has taken on sectarian overtones — a fearsome development in Syria's religiously mixed society.

Opposition figures have accused President Bashar Assad's minority Alawite regime of trying to stir up trouble with the Sunni majority to blunt the growing enthusiasm for the uprising. The protesters have been careful to portray their movement as free of any sectarian overtones.
Sectarian warfare would be a dire scenario in Syria, evoking painful memories of the worst days of the Iraq war. The Syrian regime's supporters have exploited those fears by portraying Assad as the only force that can guarantee law and order.

Human rights groups say more than 1,600 people have been killed in Assad's crackdown on a largely peaceful protest movement. But authorities blame the unrest on gunmen and religious extremists looking to stir up sectarian strife.
An offshoot of Shiite Islam, the Alawite sect represents about 11 percent of the population in Syria. The sect's longtime dominance has bred seething resentments, which Assad has worked to tamp down by enforcing a strictly secular identity in Syria.

But now, Assad is relying heavily on his Alawite power base to crush the uprising.
The Assad family has ruled Syria for more than four decades with Bashar, and his father, Hafez, before him, leading one of the most authoritarian regimes in the Middle East. The uprising, which kicked off in mid-March, is the most potent threat the Assad family dynasty has ever faced.

On Thursday, Syrians held general strikes across several cities in what has become a weekly ritual one day before tens of thousands take to the streets for protests following Friday prayers. The strikes are part of a strategy to squeeze the economy as Assad struggles to put down the uprising.

So far, the opposition has yet to bring out the middle and upper middle classes in Damascus and Aleppo, the two economic powerhouses. But there will be little to prop up the regime if business comes to a halt, private enterprises go bankrupt and the government cannot pay state employees.
The violence in Syria has drawn widespread international condemnation.

On Thursday, the German Foreign Ministry said "the siege of the city of Homs" must end.
"All of the concerned population must be granted access to medical care," the statement said. "Syria must finally honor the basic human and civil rights to which it has committed itself under international law."
The United States and France both angered the regime two weeks ago when their ambassadors traveled to the central city of Hama, a bastion of opposition support.

Syria warned the envoys this week not to travel outside the capital without permission.
French Foreign Ministry spokesman Romain Nadal dismissed the warning Thursday and said it illustrates "the isolation ... of the Syrian regime."

Nadal told an online briefing, "it is naturally part of the role of ambassadors to move around in the countries where they reside." He noted that Syria's ambassador to France can travel where she wants.
The U.S. State Department said the Syrian order reflected a government that has something to hide.
Also Thursday, a group of lawyers in the southern Syrian village of Sweida said security forces did not intervene as regime supporters attacked them.

Lawyer Alaa Saimoua said up to 60 lawyers had gathered at their office to discuss ways to protest attacks against lawyers by pro-regime gunmen known as "shabiha" that occurred few days earlier.
"We were besieged for six hours," he said. "When we tried to go out, we were attacked by shabiha who beat some lawyers and threw stones at the building, smashing its windows, all under the eyes of security forces."
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AP writers Zeina Karam in Beirut and Juergen Baetz in Berlin contributed to this report.