BETHLEHEM (Ma'an) -- Forces loyal to Syrian President Bashar Assad on Thursday bombed a hospital in Damascus' Yarmouk refugee camp, Palestinian sources told Ma'an.

Sources in the camp told Ma'an that that there have been heavy clashes between Assad's troops and opposition forces around the Palestine hospital since Monday morning, and that Assad's forces shelled the building twice on Thursday causing a huge fire.

Palestinians in Yarmouk told Ma'an that the Syrian army was targeting the hospital because medics were treating wounded from all sides, while Assad's regime only allowed its soldiers to be treated.

They added that fighting in Yarmouk was intensifying daily, and that the number of Palestinians killed was rising dramatically in camps across Damascus and in Daraa and Halab.

A resident of Yarmouk told Reuters on Thursday that the army seemed to be targeting sites on the edges of the camp, firing shells every minute. The bombardment started around 7 a.m. and was still going three hours later.

Yarmouk is the largest Palestinian refugee camp in Syria.

Damascus and Syria's second biggest city, Aleppo, came under shell fire on Thursday as Assad's forces stepped up efforts to crush rebels threatening the government's two main power centers.

One of the most senior figures to defect from Assad's inner circle, Brigadier General Manaf Tlas, put himself forward as someone who could help unite the fragmented opposition inside and outside Syria on a blueprint for a transfer of power.

A bomb attack that killed four of Assad's closest lieutenants last week prompted predictions among his enemies that the 46-year-old president's time in power was drawing to a close.

But in the days that have followed that attack, Assad's forces have noticeably toughened their response to the armed revolt, with fixed-wing combat aircraft seen in action over Aleppo and rebel fighters said by opposition sources to have been summarily executed on the streets of Damascus.

Military experts believe an overstretched Syrian army is pulling back to concentrate on Aleppo and Damascus, while leaving outlying areas in the hands of rebels.

In its most recent comment on the fighting, state-run Syrian television said on Wednesday that government troops were imposing security and stability in and around Aleppo.

Assad himself has not spoken in public in more than a week since the Damascus bomb attack on his inner circle, confining himself to appearing at formal televised events.

Western powers have been calling for Assad to be removed from office for months, but they fear that he will fight to the end, raising the risk of sectarian warfare spreading across one of the world's most volatile regions.

UN Secretary-General Ban Ki-moon, addressing the Bosnian parliament in Sarajevo, said the world must unite to end the "slaughter" in Syria, recalling the inertia of the United Nations in 1995 during the Srebrenica massacre in Bosnia.

At the UN Security Council, members blamed each other for rising violence in Syria. Western states pledged to seek an end to the conflict outside the world body, while Russia warned of "likely catastrophic consequences" with that approach.

Russia, an ally of Syria, and China have repeatedly blocked Western-backed Security Council resolutions on Syria.

Reuters contributed to this report.