BEIRUT -- A new wave of airstrikes and shelling on eastern suburbs of the Syrian capital Damascus left at least 22 people dead and dozens wounded Saturday, raising the death toll of a week of bombing in the area to 500, as the UN Security Council unanimously approved a resolution demanding a 30-day ceasefire across Syria.

The weeklong bombardment has overwhelmed rescuers and doctors at makeshift hospitals, many of which have also been bombed. Activists say that terrified residents have been hiding in underground shelters where dozens of people can be crammed into small places.

The latest wave of bombings came after the UN Security Council delayed a vote on a resolution demanding a 30-day humanitarian ceasefire across Syria in hopes of closing a gap over the timing for a halt to fighting.

Council members met at noon EST on Saturday and resumed negotiations ahead of an expected vote.

As she headed into the meeting, U.S. Ambassador Nikki Haley said: "Today we are going to see if Russia has a conscience."

Ambassador Karel Van Oosterom of The Netherlands said there had been "extensive contacts" with Russia overnight.

Russia's UN Ambassador Vassily Nebenzia had called an immediate ceasefire unrealistic, and in an apparent bid to get Russian support, sponsors Kuwait and Sweden amended the draft resolution to drop a demand that the ceasefire take effect 72 hours after the resolution's adoption.

Later Saturday, the UN Security Council unanimously approved a resolution demanding a 30-day ceasefire across Syria "without delay" to deliver humanitarian aid to millions and evacuate the critically ill and wounded.

"The UN convoys and evacuation teams are ready to go," said Sweden's UN Ambassador Olof Skoog.

Russia has been a main backer of Syrian President Bashar Assad since the country's conflict began seven years ago. In 2015, Moscow joined the war on Assad's side tipping the balance of power in his favour.

Syrian opposition activists say Russian warplanes are taking part in bombarding Damascus' eastern suburbs, also known as eastern Ghouta, where many people are hiding in underground shelters with little food and medical supplies amid a tight government siege.

"There is no electricity, no water, no flour, no bread and no baby formula," said paramedic Siraj Mahmoud in an audio message calling for a short break in airstrikes so residents can get food for their children, "There is nothing inside Ghouta."

Syrian opposition activists said that government forces used phosphorous bombs in their attacks on the suburbs, but the claims could not be independently confirmed.

The Britain-based Syrian Observatory for Human Rights said airstrikes that hit several suburbs left 22 people dead in different areas, including 10 in the suburb of Douma.

The opposition's Syrian Civil Defence, also known as the White Helmets, said 23 people were killed.

The Observatory said that since the latest wave of bombardment began Sunday, 510 civilians, including 127 children and 75 women, have been killed in eastern Ghouta.

The White Helmets said it has documented the names of 420 people who have been killed since Sunday, adding that dozens more have still not been identified.

Syrian state media reported that rebels fired mortar shells on Damascus, Assad's seat of power, killing at least one person and wounding seven.

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Edith M. Lederer contributed to this report from the United Nations.