An aid convoy intended to bring food and basic medicines to desperate Syrian civilians in Eastern Ghouta was stripped of vital medical supplies as it entered the besieged rebel-held suburbs.

Syrian government authorities removed most medical supplies from the trucks, preventing trauma kits, surgical supplies, insulin and dialysis equipment from reaching the battered enclave of 400,000 people, the World Health Organisation (WHO) said.

Eastern Ghouta has been under siege by government forces since 2013 and the United Nations feared people inside were running out of food and medicine even before a major assault began two weeks ago.

“The health supplies provided by WHO in these convoys are selected after extensive consultations with health partners working in these areas and are desperately needed to save lives and reduce suffering,” a WHO spokesperson told The Independent.

The convoy consisted of 46 truckloads of heath and nutrition supplies, along with food for 27,500 people, the UN’s Office for the Coordination of Humanitarian Affairs said.

It is the first aid delivery to reach the region in nearly three weeks.

Eastern Ghouta bombings: Syrian war in pictures Show all 14 1 /14 Eastern Ghouta bombings: Syrian war in pictures Eastern Ghouta bombings: Syrian war in pictures A Syrian woman and children run for cover amid the rubble of buildings. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Smoke rises from buildings following the attack on the village of Mesraba in the rebel-held besieged Eastern Ghouta region on the outskirts of the capital Damascu. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Injured children receive medical treatment. EPA Eastern Ghouta bombings: Syrian war in pictures A Syrian man carries a child injured. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures An injured child receives treatment following bombings on several areas of eastern Ghouta. EPA Eastern Ghouta bombings: Syrian war in pictures A child reacts inside a hospital after relatives were injured in the bombing. EPA Eastern Ghouta bombings: Syrian war in pictures Syrian children cry at a make-shift hospital in Douma following air strikes on the Syrian village of Mesraba. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Syrian Civil Defense group extinguishing a store during airstrikes and shelling by Syrian government forces. AP Eastern Ghouta bombings: Syrian war in pictures A wounded 12-year-old Syrian boy, cries as he receives treatment at a make-shift hospital. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures Syrians carry a wounded man. AFP/Getty Eastern Ghouta bombings: Syrian war in pictures An injured man covered with blood at a medical point. Reuters Eastern Ghouta bombings: Syrian war in pictures People sit a medical point in the besieged town of Douma, Eastern Ghouta. Reuters Eastern Ghouta bombings: Syrian war in pictures Syrian Civil Defense running to help survivors. AP Eastern Ghouta bombings: Syrian war in pictures Injured children receive medical treatment. EPA

Syrian President Bashar al-Assad has vowed to continue his military push into Eastern Ghouta, the biggest opposition stronghold remaining near the capital, Damacus.

He said the offensive did not contravene the five-hour ceasefires arranged each day by his main ally, Russia.

The Syrian Observatory for Human Rights, a UK-based war monitor, said over 700 people had died in two weeks of intense bombardment, many of them children.

Pro-Assad forces have made sudden advances into Eastern Ghouta in recent days, capturing a third of the area, the office said, bringing them closer to cutting it in two.

In comments broadcast by state television on Sunday, Mr Assad dismissed Western statements about the humanitarian situation in Eastern Ghouta as “a ridiculous lie”.

Boris Johnson suggests the UK could strike Syria in response to Assad's attack on eastern Ghouta

Moscow made a similar case at the UN Human Rights Council in Geneva. “The media atmosphere is saturated with lies,” Russian diplomat Alexei Goryaev said.

“As a result we see debates and votes that are entirely removed from the actual situation on the ground.”

A Syrian civil defence volunteer carries children as he helps them try to flee their homes in the town of Hamouria in Syria’s besieged Eastern Ghouta (AFP/Getty)

Russia’s military said the rebels in control of Eastern Ghouta had agreed to let civilians leave in return for aid.

Both Assad and Russia have repeatedly accused the rebels of stopping civilians from fleeing Eastern Ghouta, a charge denied by the insurgents, who say people there fear arrest, torture or forcible conscription if they cross into government areas.

A boy walks near damaged buildings in the besieged town of Douma in Eastern Ghouta in Damascus (Reuters)

Also on Sunday, the United States made its strongest accusation to date about Moscow’s complicity in civilian deaths in Syria, saying Russian aircraft flew bombing missions over Eastern Ghouta in defiance of a 30-day United Nations ceasefire.

“Russia has gone on to ignore the UN ceasefire’s terms and to kill innocent civilians under the false auspices of counter-terrorism operations,” the White House said in a statement.

It called on Mr Assad to “immediately cease targeting medical infrastructure and civilians”.

Russia says the UN ceasefire does not apply to rebel groups in Eastern Ghouta, who Moscow considers members of terrorist groups banned by the UN.