BEIRUT (AP) — World leaders called for an urgent cease-fire in Syria on Thursday as government forces pounded the opposition-controlled eastern suburbs of the capital in a crushing campaign that has left hundreds of people dead in recent days.

The U.N. Security Council was expected to vote on a resolution, called for by Sweden and Kuwait, ordering a cease-fire to allow relief agencies to deliver aid around Syria and evacuate the critically sick and wounded from besieged areas to receive medical care.

In the rebel-held suburbs of Damascus known as eastern Ghouta, medical workers said they hadn't been able to see their families for days as they worked round the clock at hospitals that have been moved underground to protect them from bombing, while their spouses and children stay in shelters.

"You can't be above ground for even 15 minutes," said a nurse in the town of Kafr Batna, who spoke on condition of anonymity to protect the identity of family members still living in government areas. "At any moment I expect to have to treat my relatives for wounds," he said.

In the background the deep boom of a bomb could be heard exploding as the nurse spoke by Skype to The Associated Press. He said a barrel bomb had fallen less than half a kilometer (one-third mile) away.

A spokesman for the Syrian Civil Defense search-and-rescue group said eastern Ghouta was being targeted for "extermination."

"This is a war against civilians," said the spokesman, Siraj Mahmoud. "The civil defense is being targeted as they rescue women and children, evacuate civilians from targeted areas and put out fires."

Four rescue workers of the organization, also known as the White Helmets, have been killed since Sunday, Mahmoud said.

Russia's U.N. Ambassador, Vassily Nebenzia, called a 30-day cease-fire unrealistic, but Moscow said it would consider supporting the U.N.-proposed truce if it doesn't cover extremists such as the Islamic State group and al-Qaida-linked groups.

Foreign Minister Sergey Lavrov said al-Qaida-linked fighters were using civilians as human shields in the rebel-held suburbs outside Damascus.

Al-Qaida's Syria affiliate is not known to have many fighters in eastern Ghouta, and government forces on Thursday concentrated their fire on hospitals, ambulances, apartment blocks and other civilian sites, according to rescue workers, war monitors, human rights groups, and several videos emerging from the war-scarred region.

U.N. Secretary-General Antonio Guterres called for an immediate suspension of "all war activities" in the area where he said people were living "in hell on Earth."

The Britain-based Syrian Observatory for Human Rights monitoring group said 400 people, including dozens of children, have been killed since Sunday.

The Russian military is again supporting Assad's forces in the assault on eastern Ghouta, as it did in the campaign to retake the rebel-held half of Syria's largest city, Aleppo, in late 2016, which drove the rebels from their enclave there. Then as now it cited the presence of al-Qaida-linked groups as grounds for the sweeping operation.

German Chancellor Angela Merkel called on the European Union to step up pressure on Russia and Iran to end the violence in Syria.

"The regime is not fighting against terrorists, but against its own people, killing children, destroying hospitals, and this is a massacre to be condemned," she told Parliament.

Besides President Bashar Assad, Merkel said "Iran and Russia have a particular responsibility" as they are both supporting the government forces. She said Germany's foreign minister plans to talk directly with his Russian counterpart and called for other EU nations to do what they can.

"We need to do everything in our power to put an end to this massacre," she said.

Lavrov said in remarks in Belgrade, Serbia, that an al-Qaida-linked group blocked a proposal by Russia's military earlier this week to allow opposition fighters to leave eastern Ghouta in exchange for ending the government's offensive.

That contradicted an assertion by one of the largest rebel groups in eastern Ghouta, which told the AP earlier this week that Russia refused to allow al-Qaida fighters to leave in November, accusing Moscow of wanting to keep the fighters there as a pretext for a comprehensive military campaign.

The International Committee of the Red Cross said it was "shocked" by the level of violence and called for immediate access to civilians in besieged rebel-held areas.

Robert Mardini, ICRC's regional director of the Near and Middle East, told reporters in Beirut that the agency has a convoy of food, medicine and medical supplies ready to be delivered to eastern Ghouta.

Russian news reports said Moscow has beefed up its forces in Syria with several warplanes, including its latest fighter jets. The Kremlin wouldn't comment on the reports, referring questions to the military, which has remained mum about the deployment.

Russia has rejected allegations it was responsible for the mounting civilian casualties in eastern Ghouta, but anger is mounting along with the death toll.

On Thursday, scores of protesters, including prominent Syrian opposition figures, gathered outside the Russian Consulate in Istanbul, chanting, "Russia get out of Syria" and "Iran get out of Syria" in Turkish and Arabic.

Syria's conflict, which has killed more than 400,000 people and displaced millions in the past seven years, has escalated in recent weeks as Assad and his allies push to retake remaining rebel-held areas in the country.

Turkey has also opened a new front against Syrian Kurdish fighters in the north, launching an air and ground offensive on the Kurdish-controlled enclave of Afrin last month.

Hundreds of pro-Syrian government fighters entered Afrin this week as part of an agreement with the Kurdish militia, known as the YPG, to bolster resistance to Turkey's assault.

Hundreds of people gathered in Afrin's main square on Thursday, celebrating the arrival of the pro-government fighters. TV footage showed fighters in camouflage uniforms standing among scores of men who gathered in the square waving posters of Assad.

Turkish warplanes could be heard flying overhead, sending some fleeing the area.

The pro-government daily Al-Watan said some 500 pro-government fighters of the so-called Popular Forces have entered Afrin since Tuesday, taking positions along the region's borders.

A YPG spokesman, Nuri Mehmud, said the pro-government fighters brought in armored vehicles but said more was needed to withstand Turkey's military campaign.

"There needs to be a no-fly zone," Mehmud said. "The Syrian army must protect Syrian lands."

Turkey launched the operation to uproot the YPG from Afrin on Jan. 20, saying the group is linked to a Kurdish insurgency inside its own borders.