Smoke rises after the Syrian military reportedly dropped a barrel bomb over the city of Daraya. (Fadi Dirani/AFP/Getty Images)

A sharp increase in Syrian government airstrikes against rebel-held areas of Aleppo in recent days prompted a fresh exodus of civilians from the northern city Wednesday and appeals from the Syrian opposition for tougher international steps against President Bashar al-Assad’s regime.

The escalation in violence has coincided with the beginning of long-awaited peace talks in Switzerland last month and cast further doubt on the likelihood that the already deadlocked negotiations will end the bloodshed engulfing Syria.

More than 700 people have died in Aleppo in the two weeks since the peace talks began, the highest toll recorded since rebels captured about half of Syria’s commercial capital from the government in July 2012, according to the Britain-based Syrian Observatory for Human Rights. The Syrian Opposition Coalition put the death toll at 1,242.

The vast majority of the victims were civilians killed in so-called barrel bombings, in which barrels packed with explosives, fuel and debris such as nails are dropped from helicopters or planes. The crude but highly effective bombs lack precision and have the power to demolish entire buildings.

With an average of 20 barrel bombs falling on the city daily since the peace talks began, whole blocks have been reduced to rubble and neighborhoods have been emptied, activists said.

“Aleppo is not the same Aleppo that it used to be. It’s a ghost town, it’s a town destroyed completely,” said Laith al-Halabi, 20, a citizen journalist who takes photographs of the aftermath of attacks.

Government forces also have begun dropping barrel bombs over other rebel-held parts of the country, including the Damascus suburb of Daraya, where a video posted on YouTube last week captured their devastating impact. The Syrian Observatory said more than 2,000 people have died nationwide since the peace talks started on Jan. 22 with much fanfare by top world diplomats at a conference in the Swiss resort town of Montreux.

But it is in Aleppo that the increase in violence has been felt most. Thousands of residents have fled over the past two days as the attacks intensified, most of them crossing the front line dissecting the divided city to seek refuge in the government-held west, activists and human rights groups say.

Nearly 10,000 people also have streamed toward Turkey, according to Turkish news reports, swelling a crowded refugee camp on the Syrian side of the border at the crossing point of Bab al-Salameh. Turkey, which already is hosting an estimated 700,000 of the region’s 2.46 million Syrian refugees, admits only the minority of Syrians who have passports.

Barrel bombs were dropped on five Aleppo neighborhoods on Tuesday, killing at least five people, according to the Syrian Observatory. Activists attributed the relatively low toll to the fact that so many people have fled. The official Syrian news agency SANA reported that an unspecified number of “terrorists” had been killed in the five neighborhoods, and offered no further details.

The attacks have diminished hope among ordinary Syrians that the Geneva peace talks, set to resume Monday after a week-long break, will help end the conflict. Instead, fears are mounting that the government is preparing to retake the rebel-held portion of the city, said Rifaat Rifai, an Aleppo journalist who is living in Turkey.

The rebels have been weakened by the bombings and by the past month of infighting between the al-Qaeda-inspired Islamic State of Iraq and Syria and more moderate units, Rifai said. “Fears that the regime might storm the city are one of the reasons why many families are fleeing,” he said.

Halabi said the government is trying to recapture territory to strengthen its hand at the negotiations. “The regime wants to recapture Aleppo to prove its power and force its own conditions at Geneva,” he said.

Also Wednesday, the Syrian government missed another deadline for handing over its chemical weapons under the terms of an agreement reached last year with the United Nations. The deal averted threatened U.S. airstrikes to punish Syria for allegedly killing hundreds of civilians in a chemical weapons attack.

Syrian Deputy Foreign Minister Faisal Mekdad described Syria’s cooperation on the dismantling of the chemical weapons program as “exemplary” and blamed the delays on terrorism.

“Difficulties facing Syria, particularly in the framework of the country’s war on terrorism, could hinder the implementation of some commitments from time to time,” SANA quoted him as saying.

But the Syrian opposition said the delay demonstrated that Assad is not to be trusted, and called on the U.N. Security Council to threaten measures including the use of force if Syria does not comply.

“The international community should realize that the Assad regime is not a credible partner,” the opposition coalition said in a statement.