ALEPPO, Syria, April 29 (UPI) -- As more bombs rained down on Aleppo on Friday morning, United Nations officials admitted that the situation in Syria's largest city is "catastrophic."
Warplanes launched a fresh wave of airstrikes targeting rebel-held parts of Aleppo, raising fears of more casualties.
Religious leaders were forced to suspend Friday prayer sermons, according to the Syrian Observatory for Human Rights and the Local Coordination Committees, who report at least three people killed and several injured in the latest attacks.
Rebels shelled a mosque in the government-held district of Bab al-Faraj, killing eight people, state media is reporting. A clinic in rebel-held Marja was targeted in an airstrike.
Earlier this week there was outrage after at least 27 people died when the Medecins Sans Frontieres-backed al-Quds hospital was hit by bombs. There were at least 30 more fatalities in other attacks.
He added: "The stakes are so incredibly high because so many civilian lives are at stake, so many humanitarian health workers and relief workers are being bombed, killed, maimed at the moment that the whole lifeline to millions of people is now also at stake.
"Doctors have been killed, health workers have been killed and medical workers have been blocked from coming to their patients."
Medecins Sans Frontieres said at least 14 patients and three doctors had been killed in the airstrike on al-Quds hospital, including Mohammed Wasim Moaz, one of the city's last pediatricians. He had worked at the hospital since 2013.
"He kept it going, was always there and always worried about the needs of the people. He was honest and very committed. He worked in conditions you cannot even begin to imagine," an MSF representative, Aitor Zabalgogeazkoa, told the BBC.
It is still unclear who is behind the latest bombing campaign. Local sources blame the Syrian military or Russia, which is supporting the government of President Bashar al-Assad.
But the Syrian military denied targeting the hospital.
"Such news is merely an attempt to cover up terrorist crimes which target peaceful citizens in Aleppo," a military source reportedly told state TV.
The Russian defense ministry insists that it has not carried out any bombings in Aleppo in recent days, according to Russian news agencies.
U.S. Secretary of State John Kerry stated that he was "outraged" by the hospital attack.
"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," he said.
Meanwhile, the Syrian government has denounced as an "illegitimate intervention" the reported arrival of 150 U.S. troops in the town of Rmeilan in the predominantly northern Kurdish province of Hassakeh.
This comes a week after U.S. President Barack Obama said that he was deploying 250 troops to Syria to help certain rebel groups fight the Islamic State, which means that 300 American troops are now in Syria.