UNITED NATIONS — The United States on Wednesday sought UN Security Council support for action to hold Iran "accountable" for an alleged plot to assassinate the Saudi ambassador to Washington, diplomats said.

France and Britain have already given strong backing to the US government. But the US administration will also be sending delegations to Beijing and Moscow to give details of the investigation, diplomats said.

US ambassador Susan Rice, joined by the Saudi envoy to the UN, Abdallah Al-Mouallimi, held separate meetings with envoys on the 15 nation council, US officials and diplomats said.

Representatives from the Federal Bureau of Investigation, Central Intelligence Agency and Department of Justice briefed envoys.

The aim was to "solicit their support in holding Iran accountable," a US official said on condition of anonymity. Iran has strongly denied and condemned the allegations made by the US Justice Department.

The United States has not yet decided whether it will seek Security Council action against Iran however, diplomats who attended the meetings said.

The US Justice Department on Tuesday charged two men with conspiring with Iranian officials to assassinate Saudi ambassador to the United States, Adel al-Jubeir.

Iran, which faces four rounds of UN Security Council sanctions over its nuclear program, called the US allegations part of an "evil plot" against the Islamic Republic, and in a letter of protest to the UN Security Council accused Washington of "warmongering."

Rice was quoted as saying that US delegations would go to Russia and China to lay out the US case. Both nations normally oppose punitive action against individual countries.

Russia's UN ambassador Vitaly Churkin called the case "rather bizarre" in comments to reporters.

Britain and France have already indicated they would back the US moves.

"For France, this is an extremely serious affair, an outrageous violation of international law, and its perpetrators and backers must be held accountable," French foreign ministry spokesman Bernard Valero said in Paris on Wednesday.

Britain would support "measures to hold Iran accountable for its actions," said a spokesman for British Prime Minister David Cameron.

The spokesman called the alleged plot "shocking".

"The United Kingdom is in close touch with the US authorities on this case. We will support measures to hold Iran accountable for its actions."

"We congratulate the US authorities on the successful operation to disrupt a conspiracy to attack diplomats in the United States," the spokesman said.