The United Nations' under-secretary-general for humanitarian affairs has accused the Syrian government of "severely" curtailing humanitarian aid efforts in the country. Stephen O'Brien slammed the authorities while addressing the UN Security Council in Geneva on 26 May.

"The Syrian government has severely curtailed the UN's ability to reach those in need," he said. "A convoy and assessment mission to Darayya [the suburbs of Damascus], where 4,000 civilians have been besieged for almost four years, scheduled for 12 May, had to be aborted due to unconscionable last minute restrictions imposed by government security forces."

He also called for an immediate end to sieges by warring Syrian factions, with nearly 600,000 civilians besieged across the country despite the official ceasefire. O'Brien described these tactics as a "weapon of war" and "reprehensible".

Of the estimated 592,700 besieged in the country, around 452,700 are thought to be in the suburbs surrounding Damascus. According to O'Brien, this has caused humanitarian aid to be blocked and allowed civilians to starve.

The O'Brien was speaking after visiting Syrian refugees on the Turkish border town of Reyhanli. There he met civilians who were severely injured in an air strike on Al-Quds Hospital in Syria on 27 April. One of those was paediatrician Muhammad Waseem Maaz.

"I sat down at Dr Maaz's bedside as he struggled for life with appalling and severe brain, abdominal and facial wounds after he was struck by an airstrike on Al-Quds Hospital in the east of Aleppo on 27 April, as he was bravely himself saving lives," said O'Brian.

He added, "A bare whisper is all he could muster: 'Please, peace'". In the speech, O'Brien also recommended air drops of humanitarian aid to besieged areas in Syria.

Syria: Videos show ongoing air strikes on Homs countryside IBTimes UK