A senior U.S. diplomat says it has become "more challenging" for Washington to work with Moscow in Syria amid Russia's resistance to a call by Western powers for a 30-day cease-fire in the war-torn country.
"We've worked hard to maintain relations and a dialogue with Russia on those issues and areas where we can work cooperatively toward a common goal. Syria is one," U.S. Deputy Secretary of State John Sullivan told reporters in Brussels on February 23.
"As the campaign against [Islamic State militants] has proceeded, it has become more challenging for us to work with the Russians [there]," he added.
His comments came ahead of a planned vote in the United Nations Security Council on a resolution demanding a 30-day cease-fire across Syria to allow delivery of humanitarian aid and to evacuate ill and wounded civilians.
The leaders of France and Germany urged Russian President Vladimir Putin to back the truce, but Moscow has resisted, saying it wanted "guarantees" it would be respected by U.S.-backed rebel fighters.
The vote had been scheduled for early on February 23 but has twice been delayed as Western diplomats negotiate to avoid a Russian veto.
The developments come amid a growing outcry from Western capitals, the United Nations, and humanitarian groups over Syrian government air strikes and shelling that have pounded a rebel-held suburb of Damascus for the past six days, killing an estimated 450 people.
Russia has given President Bashar al-Assad's government crucial support throughout the 7-year-old war in Syria and has generally rejected moves it feels would put its Syrian ally at a disadvantage.