President George W. Bush spoke with Russian President Vladimir Putin on Monday as the United States tries to convince Russia and China that the UN Security Council must take tougher action to curb Iran's nuclear program.

White House spokesman Scott McClellan declined to give details of the telephone conversation, but said: "The two leaders stressed the importance of preventing Iran from obtaining nuclear weapons."

He said they agreed to remain "in close contact on this important priority."

German Chancellor Angela Merkel failed to win Putin's approval for UN sanctions at a meeting last week but she was hopeful that Russia eventually would not block tougher measures. Merkel is to meet Bush in Washington this week.

Senior officials from the permanent UN Security Council member states -- Britain, China, France, Russia and the United States -- as well as Germany are to meet in Paris on Tuesday to prepare for a meeting of the countries' foreign ministers on Iran in New York on May 9.

The United States, Britain and France want to introduce a UN Security Council resolution requiring that Iran stop uranium enrichment or face possible sanctions.

Russia and China have so far opposed sanctions and Iran has said it would ignore any U.N. Security Council resolution against its nuclear program.