Site of regime bombing in Aleppo
Site of regime bombing in AleppoReuters

The United Nations' top aid official voiced anger on Monday at world powers' inability to agree on a truce to allow aid into Aleppo, warning of an "unparalleled" humanitarian catastrophe in the battleground Syrian city.

Stephen O'Brien told the UN Security Council that plans were in place to quickly send 70 trucks loaded with humanitarian aid to eastern Aleppo if all sides agreed on a truce.

"I'm not going to pretend. I'm angry, very angry," O'Brien told council members holding their third meeting on the crisis in Aleppo this month.

"As the UN's humanitarian chief, this callous carnage that is Syria has long since moved from the cynical to the sinful," he continued, renewing his call for a 48-hour pause in fighting in Aleppo, where the violence escalated sharply in July when regime forces surrounded the rebel-held east.

Up to 275,000 people in eastern Aleppo have been almost entirely cut off from food, water, medicine and electricity for over a month, while 1.5 million people living in the west of the city also face severe shortages.

"In Aleppo, we risk seeing a humanitarian catastrophe unparalleled in the over five years of bloodshed and carnage in the Syrian conflict," said O'Brien.

The war-torn nation's second city "has become the apex of horror" for suffering Syrians, he said.

O'Brien welcomed the announcement from Russia, Syria's key ally, that it supports the call for the 48-hour ceasefire, but said all sides must sign on.

Once the needed security assurances are received, UN aid workers are ready to move 50 trucks of aid from western Aleppo to the east, and an additional 20 trucks from Turkey into eastern Aleppo, he said.

O'Brien urged all countries with influence, in particular the United States and Russia, which co-chair the international group backing the peace process in Syria, to rapidly reach agreement on a ceasefire deal.

Not a single aid convoy has reached Syria's besieged areas in August while air strikes have hit hospitals and schools.

In July alone, there were 44 attacks on medical and health facilities throughout Syria, including attacks against five out of the nine hospitals in eastern Aleppo, according to the UN. The battle for Syria's second city has killed 333 civilians since July 31.

More than 290,000 people have been killed in the Syrian war that erupted in March 2011 and international efforts to end the conflict have faltered.

AFP contributed to this report.