Tuesday's meeting of deputy foreign ministers of the UN Security Council's five permanent members - the United States, Britain, France, China and Russia - plus Germany, was called after Tehran declared last week that it had enriched uranium and was aiming for industrial-scale production.
Also on Tuesday, George Bush, the US president, said he would discuss Iran's nuclear activities with Hu Jintao, China's president, who has been cool towards sanctions, when they meet on Thursday.
Asked if his options included planning for a nuclear strike, Bush said: "All options are on the table. We want to solve this issue diplomatically and we're working hard to do so."
Washington believes Iran is trying to build bombs but Tehran says it is only developing nuclear energy.
The United States, which already enforces its own sanctions on Iran, wants the Security Council to be ready for strong diplomatic action, including measures such as a freeze on assets and visa curbs on Iranian officials.
Tehran had vowed to continue its pursuit of nuclear technology, whatever the meeting's outcome.
Iran's foreign ministry spokesman, Hamid Reza Asefi said: "Whatever the result of this meeting might be, Iran will not abandon its rights."
Sean McCormack, the US State Department spokesman, stressed that the goal of the Moscow meeting was to make preparations for decisions to be taken in various capitals.
The International Atomic Energy Agency is due to report at the end of the month on whether Iran is complying with UN demands that it halt uranium enrichment.