Six countries mediating in a longstanding nuclear dispute with Iran will gather in Paris on Saturday to discuss new tougher sanctions against the country, the U.S. State Department said on Thursday.

The United States is expressing disappointment over what officials said was a lack of urgency shown by China and Russia in big-power talks on new sanctions against Iran over it nuclear program. Senior diplomats of the five veto-wielding U.N. Security Council member countries and Germany, the P5+1, discussed the issue Friday in London.

The U.N. Security Council will implement a third set of sanctions if Iran fails to answer key questions on its nuclear program.

Representatives from six world powers meeting in London agreed Friday to push ahead with a third round of sanctions against Iran, unless it quickly shows greater transparency with regard to its nuclear research program.

Deputy foreign ministers of six world powers will meet in London on Friday to discuss a possible third round of sanctions against Iran over its refusal to abandon uranium enrichment.

Hardline President Mahmoud Ahmadinejad on Thursday warned European countries not to follow the U.S. lead in imposing unilateral sanctions against his country, state radio reported.

The world's major powers have agreed to delay a vote on tougher sanctions on Iran until late November at the earliest, depending on reports by the UN nuclear watchdog and a European Union negotiator.

The United States is hosting a high-level diplomatic meeting in Washington Friday to discuss the possibility of imposing new U.N. sanctions against Iran over its alleged nuclear weapons program.

Russia is concerned by media reports that military action against Iran could take place soon, the acting Russian foreign minister said Tuesday.

The State Department says Iran's continued defiance over its nuclear program should be met with more sanctions resolutions in the U.N. Security Council.

A senior U.S. diplomat warned Iran that it is facing the prospects of tough new sanctions "in the next week or two" unless it comes to the negotiating table on its nuclear program.

An Iranian official says his country will not stop developing its nuclear program even if the United Nations imposes a third set of sanctions.