British Prime Minister Gordon Brown said Monday that tougher sanctions are likely against Iran over its contested nuclear program and declined to reject outright the prospect of future military action.

Brown, holding his first Downing Street press conference, said he believed sanctions aimed at persuading Iran to halt uranium enrichment were working, but predicted a swift new U.N. Security Council resolution aimed at increasing pressure on Iranian President Mahmoud Ahmadinejad.

"I'm not one who is going forward to say we rule out any particular form of action," Brown said, asked if he would rule out options for future military action against Iran.

"But I firmly believe that the sanctions we are imposing on Iran are sanctions that are having an effect already," he said. "There will probably be a further resolution in relation to Iran soon, and I believe that is a way forward that is working and will work."

The United States and some of its allies, including Britain, fear Tehran is using its civilian nuclear program as a cover to produce atomic weapons. Iran denies the charge and has rejected two U.N. Security Council resolutions requiring it to halt uranium enrichment work.

"Again, I appeal to the Iranian authorities to understand the fears that other countries have about the development of the nuclear weapons program," Brown told reporters.

He said Britain would "take whatever measures are necessary to strengthen the sanctions regime in the future."

The International Atomic Energy Agency said this month that Iran has scaled back its uranium enrichment program, signaling a possible willingness from Tehran to resolve the international deadlock.