MOSCOW — Russia said Tuesday it regretted a decision by Washington to postpone talks on an international peace conference for Syria, underlining growing diplomatic tensions over the civil war.

The State Department said Monday it had postponed the meeting between senior diplomats, scheduled for Wednesday in The Hague, because of "ongoing consultations" over an alleged chemical weapons attack in Syria.

"It is regrettable that our partners decided to postpone the Russia-U.S. meeting on calling an international conference on Syria," Deputy Foreign Minister Gennady Gatilov, who would have taken part in the talks, said on Twitter. "Working out the political parameters for a resolution in Syria would be exceptionally useful now, when the threat of [military] force hangs over this country."

The United States has served Syrian President Bashar al-Assad notice that it believes he was responsible for chemical weapons being used against civilians last week.

Russia, Assad's key ally and arms supplier, says rebel forces may have been behind the attack and has urged Washington not to use military force against Assad.

The United States and Russia, which has protected Assad at the United Nations Security Council, agreed in May to try to arrange an international conference on ending the conflict in Syria but the chances of it happening are fading.

A senior State Department official said the United States would work with Russia to reschedule Wednesday's planned meeting and that the alleged chemical weapons attack demonstrated the need for a "comprehensive and durable political solution."