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Heavy machine-gun fire rang out across the besieged Syrian city of Latakia Tuesday as the death toll from a four-day military assault rose to 35. The British foreign secretary said President Bashar Assad was losing "the last shreds of his legitimacy."

Assad has dramatically escalated the crackdown on a 5-month-old uprising since the start of the holy month of Ramadan at the beginning of August. Despite broad international condemnation, the regime has unleashed tanks, ground troops and snipers in an attempt to retake control in rebellious areas.

"The Syrian regime has besieged towns and cities across the country, using anti-aircraft guns against civilians, a disproportionate and unacceptable response to peaceful demonstrations," British Foreign Secretary William Hague said Tuesday. "He is fast losing the last shreds of his legitimacy. He must stop the violence immediately."

The military operations have targeted Latakia, the opposition stronghold of Hama, the central city of Homs, as well as the eastern city of Deir el-Zour.

The state-run SANA news agency said army units began withdrawing from Deir el-Zour Tuesday after clearing the city of "armed terrorist gangs" in an operation that lasted several days. Syrian journalists on a government-organized trip to the city saw armored personnel carriers and other military vehicles on their way out.

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Syrian troops seized control of the eastern flashpoint city last Wednesday after shelling it and carrying out a string of arrests.

In Latakia, most of the shooting Tuesday was in the city's impoverished districts of al-Ramel, al-Shaab and Ein Tamra. Al-Ramel is home to a crowded Palestinian refugee camp where many low-income Syrians also live.

"They are arresting people all the time, they took most of my friends," said a resident, who fled to a nearby, safer area on Monday. He said many people who fled al-Ramel were later arrested in Ein Tamra. "Nowhere is safe," he added, speaking on condition of anonymity for fear of reprisals.

The U.N. agency that aids Palestinian refugees say thousands of refugees have fled the camp since Assad's forces began shelling the city in an operation that started Saturday.

"A forgotten population has become a disappeared population because we have no idea of the whereabouts of as many as 10,000 refugees who fled Latakia over the last few days," said UNRWA spokesman Chris Gunness.

"We need access which is what we are calling urgently on the Syrian regime to give us," he added.

The regime insists its crackdown is aimed at rooting out terrorists fomenting unrest in the country. But various human rights groups have accused Syrian troops of firing on largely unarmed protesters and say more than 1,800 civilians have been killed since the uprising erupted in mid-March.

SANA said Tuesday that troops were pursuing "armed terrorists" from al-Ramel, arresting a number of gunmen and dismantling explosives and mines they had planted.

After months of deadlock, the Security Council finally responded to the escalating violence in Syria on Aug. 3, condemning President Bashar Assad's forces for attacking civilians and committing human rights violations in a statement approved by all 15 council nations.

U.N. human rights chief Navi Pillay plans to brief the U.N. Security Council Thursday on the rights situation in Syria, the council president said.

The London-based Syrian Observatory for Human Rights, which has a network of people on the ground, said at least 17 people were killed Monday, six of them in Latakia. The Local Coordination Committees, another activist group, said a 22-year-old Palestinian mother of two died Tuesday.

The deaths bring the total of people who have died in Latakia since Saturday to more than 35.

The other deaths Monday took place in Homs and Houla in central Syria, when security forces opened fire on protesters. A man who had been shot earlier in Deir el-Zour died of his wounds Tuesday, according to the Observatory.

Turkey's Foreign Minister Ahmet Davutoglu called Monday on Syria to immediately end the bloodshed and threatened unspecified "steps" if it fails to do so.

"If the operations do not end, there would be nothing more to discuss about steps that would be taken," Davutoglu said, without elaborating.

Turkey, a former close ally of Syria, has been increasingly frustrated with Damascus' crackdown. Davutoglu traveled to Syria last week and urged Assad to end the bloodshed. But Turkey, Syria's neighbor and important trade partner, has not joined the U.S. and Europe in imposing sanctions.

In Washington, White House spokesman Jay Carney said Assad must "cease the systematic violence, mass arrests and the outright murder of his own people," adding that the Syrian president "has lost legitimacy to lead." Carney said the U.S. would be looking to apply further sanctions against Assad's government.

The New York-based Human Rights Watch called on the European Union to freeze the arrests of Syrian national oil and gas companies and the Central Bank of Syria "until the Syrian government ends gross human rights abuses against its citizens."

Oil and gas are among Syria's main exports.