Russia and China on Monday vetoed a United Nations Security Council resolution to establish a seven-day truce in Aleppo, as Moscow argued that talks were first necessary with Washington. Russia’s UN Ambassador Vitaly Churkin said that in the past, such ceasefires “have been used by fighters to reinforce their ammunition and to strengthen their positions and this will only worsen the suffering of civilians.” The veto was Russia’s sixth in the Syria conflict, and China’s fifth, as the two nations continue to butt heads with the West on the war that has claimed nearly half a million lives. The call for a truce comes as Syrian government forces fight to seize more territory from the rebels, and as the UN warns 200,000 civilians are trapped in the besieged city with no food or water. Deputy U.S. Ambassador to the United Nations Michele Sison called Russia out for the veto, calling Churkin’s explanation a “made-up alibi.” “We have not reached a breakthrough because Russia has been more focused on preserving its military gains than helping Aleppo’s citizens,” she said. “We will not let Russia string along this Security Council while waiting for a compromise from the Russians that never seems to come,” she said.