The Security Council has failed to agree on a statement supporting the U.N. special envoy to Yemen who is trying to get Shiite rebels to back a peace deal and end the conflict in the Arab world's poorest country.

Russia's U.N. Ambassador Vitaly Churkin told reporters "the council was almost ready to make a joint pronouncement in support of the political process" when a delegation made an unacceptable demand.

Britain's deputy ambassador Peter Wilson, clearly referring to Russia, said one country wasn't supporting its own national position.

Diplomats pointed to a statement from ambassadors based in Yemen, including Russia's envoy, expressing concern at Houthi rebel plans to set up a new political council to rule the country.

U.S. Ambassador Samantha Power warned of "grave" risks if the political process fails.