Beirut (AFP) - Syria's fifth year of war was the worst yet for civilians increasingly beset by aid blockades and sieges, humanitarian groups said Friday ahead of the anniversary of the uprising.

"Russia, the United States, France and the United Kingdom must now safeguard the glimmer of hope that the ceasefire has brought to civilians, rather than 'adding fuel to the fire'," the report said, referring to a partial truce that has largely held since February 27.

"The fifth year of the Syria conflict was the worst yet for people as warring parties have continued to wreak havoc, increasingly blocked aid and placed more communities under siege," it added.

Drafted by 30 Syrian and international humanitarian organisations, including Oxfam, CARE and the Syrian American Medical Society, the report criticises UN Security Council members for failing to stop the violence -- and even fuelling it.

"UN Security Council resolutions have consistently been flouted by parties to the conflict.

"And their international backers, including permanent members of the (Council), are not only failing to ensure implementation of the resolutions but -- through inadequate diplomatic pressure, political and military support to their allies, and direct military action -- have actively added fuel to the fire of the Syria conflict," it said.

The NGOs crafted a "report card" to track which aspects of the conflict that began with anti-regime protests on March 15, 2011 had worsened, and which world powers had fuelled the deterioration.

While the UN and aid groups have demanded an end to all attacks against civilians, the report said Russia's air strikes launched in September 2015 "directly hit and damaged civilian infrastructure".

Russia says that its campaign has only struck "terrorists".

- Aid access restricted -

Titled "Fuelling the Fire: How the UN Security Council's Permanent Members are undermining their own commitments on Syria", the document also cites reports of "300 civilian casualties" in US strikes against IS.

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Russia and the United States back opposing sides in Syria's war, though both have launched aerial bombing campaigns against jihadists in the country.

The report also looks at how the lives of children in Syria have grown even more hellish.

"Despite calls from world leaders to prevent a 'lost generation'... attacks have left more than two million children in Syria out of school; an increase of 400,000 children compared with 2014," it said.

The charities criticised all sides in the conflict for restrictions on aid access.

"Air attacks and shelling have long been among the many challenges faced by humanitarian organisations working in Syria, especially in cities like Aleppo," the report said.

"We always have to be careful. When I cross checkpoints, I don't tell guards that I am an aid worker. When we do our distributions we have to make sure we don't create a crowd that could become a target for armed groups," according to an unnamed Syrian aid worker in Daraa, southern Syria, cited by the report.