A young girl is seen in the al-Riad shelter in Aleppo, Syria, on Friday. Bombing in the opposition-held portion of the city has intensified, with an estimated 244 civilians killed over the last eight days. Photo courtesy United Nations Office for the High Commission on Human Rights

ALEPPO, Syria, April 30 (UPI) -- Government forces loyal to Syrian President Bashar al-Assad are stepping up a bombing campaign in the rebel-held residential portion of Aleppo, the nation's largest city.

The Syrian Observatory for Human Rights put the death toll at 244 over the last eight days since hostilities flared between forces loyal to Syrian President Bashar al-Assad and the rebel opposition. Assad's forces control the western half of Aleppo and the rebels control most of the east.

Al Jazeera reports at least a dozen air strikes have rattled the rebel-held portion of the city since Friday.

Aleppo is Syria's large city, home to some 2 million people before the civil war broke out. While many have fled, the city still remains a significant population center located near the Turkish border. Prior to the war, Aleppo was Syria's economic hub.

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With that as the backdrop for what is at stake, and after another round of peace talks faltered, the bombing resumed from both sides, Al Jazeera reported.

One air strike in particular, which the opposition alleges was conducted by Assad's forces, leveled a hospital in the rebel portion of the city, killing 50 people. The group Doctors Without Borders had been in charge of the al Quds field hospital and several of its members, including two doctors and two nurses, were among the dead.

U.S. Secretary of State John Kerry expressed outrage at the hospital bombing.

"We are outraged by yesterday's airstrikes in Aleppo on the al Quds hospital supported by both Doctors Without Borders and the International Committee of the Red Cross, which killed dozens of people, including children, patients and medical personnel," he said in a statement. "It appears to have been a deliberate strike on a known medical facility and follows the Assad regime's appalling record of striking such facilities and first responders. These strikes have killed hundreds of innocent Syrians."

Through state-run media, the Assad government denied it had carried out the bombing. The Russian military, which has supplied air support to Assad's ground troops, also denied responsibility.

Syrian state media also reported rebels shelled a mosque in the government-held portion of the city, killing eight.

While a temporary cessation of hostilities agreement struck in February had mostly remained in effect in the capital Damascus and the coastal city Latakia, Aleppo -- home to some of the fiercest fighting since the civil war began -- has seen things getting worse.

Zeid Ra'ad Al Hussein, the U.N. high commissioner for human rights, said in a statement on Friday that "violence is soaring back to the levels we saw before the cessation of hostilities."

Al Jazeera reports journalists on the ground predict the situation will continue to worsen with more bombings and civilian casualties in the coming days.

Peace talks between the Assad government and rebel leaders in Geneva broke down after weeks to failed attempts to broker a political agreement to permanently end hostilities in the five-year civil war. Opposition leaders walked away from the table last week as the tentative cease-fire was increasingly violated by both sides.