A humanitarian aid convoy in Daraya, Syria, on June 1. (International Committee for the Red Cross via AP)

The U.N. Security Council agreed Friday to formally request Syrian approval of humanitarian airlifts of food and medical supplies to civilians in besieged areas where the government has denied access for land shipments of aid.

The agreement to make the request, which is to be made Sunday by U.N. representatives in Damascus, was reached by consensus in the council, although some members appeared to feel more strongly about it than others.

Britain, which had requested the council meeting, said land convoys allowed so far by Syrian President Bashar al-Assad have been “too little, too late.”

“Airdrops are costly, complex and risky, but we all agree now that they are the last resort and we must now use them to relieve the human suffering,” Britain’s U.N. ambassador, Matthew Rycroft, told reporters after the closed-door meeting.

“Countries with influence over the regime, like Russia and Iran, must ensure that air access is granted,” he said. “If the [Assad] regime chooses to block land access or blocks the World Food Program from delivering aid by air, then the U.K. and other” members of an international group that has demanded the access “will consider other actions.”

Rycroft said that Russia had agreed to the consensus demand and that “there’s no doubt Russia does have very significant influence over the regime.”

In an interview with Russian television, Foreign Minister Sergei Lavrov repeated Moscow’s insistence that the United States and others collaborate more closely with Russia in actions against the Islamic State. While humanitarian access was “vital,” he said, it is of “secondary importance” to the terrorist threat.

The United States and Russia are co-chairs of an international task force that set June 1 as a deadline for Assad to permit full ground access to 19 areas where aid to civilians has been blocked, primarily by surrounding government troops, in some cases for years.

U.N. officials have said that up to a half-million people remain without assistance. Airdrops and helicopter landings, using private contractors, would be administered by the World Food Program, which has said that such operations are too unsafe without guaranteed protection from government troops and air defenses.

Asked whether his government or others were prepared to use their own air forces to deliver assistance if access is denied, Rycroft said they would wait to see Assad’s response to the Sunday demand and take the matter “one step at a time.”

At the State Department, spokesman Mark Toner said that U.S. focus “remains on exerting the pressure on actors on the ground . . . to provide that secure environment” for aid delivery.