U.S. Undersecretary of State Nicholas Burns will press for a hardening of U.N. sanctions against Iran during talks in London Friday on Tehran's disputed nuclear program.

British Prime Minister Gordon Brown and France support new sanctions if Iran continues to refuse to suspend uranium enrichment, though fellow permanent U.N. Security Council members Russia and China remain skeptical.

Burns was meeting diplomats from the four other permanent Security Council members and Germany to rally support for a tougher track with Tehran, which has a deadline next month to fully disclose details of its nuclear program.

The U.S. and allies accuse Iran of using a civilian power program as cover to develop nuclear weapons. Tehran denies the charge and insists it needs the technology to generate power.

After talks Thursday in Vienna with Mohamed ElBaradei, head of the U.N.'s International Atomic Energy Agency, Burns told reporters Washington wants a third round of U.N. Security Council sanctions passed soon.

"There are sanctions being implemented ... and there will be a third Security Council sanctions resolution" if Iran continues to defy the council, Burns said.

German Foreign Minister Frank-Walter Steinmeier gave the call qualified backing on Thursday, saying Germany will support new U.N sanctions if Tehran fails to meet December's deadline to provide full details of its program.

Brown "has already said the U.K. supports a further U.N. Security Council resolution if Iran does not comply with its international obligations," Britain's Foreign Office said in a statement.