US secretary of state Mike Pompeo on Saturday said Russia and China had blood on their hands after the two countries used a veto of a United Nations security council resolution to block cross-border aid deliveries from Turkey and Iraq to millions of Syrian civilians.

“The Russian federation’s and China’s veto yesterday of a security council resolution that allows for humanitarian aid to reach millions of Syrians is shameful,” Pompeo said in a statement.

“To Russia and China, who have chosen to make a political statement by opposing this resolution, you have blood on your hands,” he added.

Russia, backed by China, on Friday cast its 14th UN security council veto since the start of the Syrian conflict in 2011.

In October, amid growing chaos in Syria, Donald Trump abruptly ordered all US troops to withdraw from the country’s north to avoid a bloody conflict between Turkey and formerly US-backed Kurdish fighters.

Vital cross-border aid to Syria suffered its latest threat after the UN security council was unable to overcome Russian and Chinese objections to the programme.

The aid, which is sent over borders at four UN approved checkpoints and without the formal permission of the Syrian regime, is seen as critical as the humanitarian crisis in Idlib and north-east Syria continues to mount.

Throughout the past fortnight, the UN security council has been considering two alternative resolutions on cross-border aid deliveries to Syria.

On Friday, Russia, backed by China, cast its veto, to block cross-border aid deliveries to millions of Syrian civilians.

The resolution drafted by Belgium, Kuwait and Germany would have allowed cross-border humanitarian deliveries for another year from two points in Turkey and one in Iraq. But Syrian ally Russia only wanted to approve the two Turkish crossings for six months.

UN diplomats are eager to reach an agreement before Christmas, fearing it will be more difficult to solve the issue close to the deadline of 10 January since in the new year there will be a new UN security council membership.

The decision to introduce cross-border aid deliveries to Syria was first made in July 2014 after the civil war made it impossible for civilians to access humanitarian aid.

The assistant secretary-general of OCHA, the UN humanitarian agency, Ursula Mueller, said the humanitarian position was worse than last year, and reducing the number of crossings was not justified.

She added: “Without the cross-border operation, we would see an immediate end of aid supporting millions of civilians. That would cause a rapid increase in hunger and disease, resulting in death, suffering and further displacement – including across-borders – for a vulnerable population who have already suffered unspeakable tragedy as a result of almost nine years of conflict.”

The UK ambassador to the UN, Karen Pierce, said: “If the UN does not help these communities, there is no evidence, no evidence at all to believe that the Syrian government either wants to or can or will provide that assistance.”

The International Rescue Committee, alongside a host of other aid agencies, has been urging the security council not to scale back on aid delivery.