The U.S. Department of State said Wednesday that Russia has taken no “demonstrable steps” to support efforts to deliver humanitarian aid to besieged towns in Syria even though it has air assets in the country along with permission to use them. Russia endorses humanitarian efforts in the war-torn nation.

The Syrian town of Daraya last Tuesday was the first besieged town to receive a Red Cross convoy carrying aid. The delivery, carried out by both the United Nations and Syrian Arab Red Crescent staff, was the first since a government-imposed siege began in 2012.

The United States, Britain and France are advocating air drops to areas inaccessible by land in order to break through the impasse caused by lack of support and access by the Syrian government and rebels.

However, Russia had pointed out the lack of effectiveness of air drops. “It’s easier said than done,” the country’s U.N. Ambassador Vitaly Churkin said last week.

State Department spokesman Mark Toner said in a statement released Wednesday that Russian Foreign Minister Sergei Lavrov was in Vienna last month when the International Syrian Support Group called for the aerial delivery of humanitarian aid to besieged Syrians towns. The deadline for access, set for June 1, has since passed.

“We are obviously disappointed, to put it mildly, that ... Russia has not taken any demonstrable steps to support the International Syria Support Group's call for the delivery of humanitarian relief by air,” Toner said. Although he declined to specify if any direct talks had been carried out with Moscow, he added, “They're aware of our concerns.”

Syrian President Bashar Assad Tuesday vowed to fight until he took back “every inch” of the country from his foes. In response to that, Toner said the Syrian leader was “sadly mistaken if he thinks there’s a military solution.”