LONDON (Reuters) -British Prime Minister Gordon Brown said on Monday he would not rule out military action against Iran, but believed a policy of sanctions could still persuade Tehran to drop its disputed nuclear program.

“I firmly believe that the sanctions policy that we are pursuing will work, but I’m not one who’s going forward to say that we rule out any particular form of action,” Brown told a news conference, when asked if he would rule out a military strike against Iran.

The United Nations Security Council has imposed two rounds of sanctions since December on Iran for failing to halt uranium enrichment, a process which can produce fuel for power plants or material for warheads. A third sanctions resolution is being considered.

Western powers suspect Iran’s activities are secretly aimed at producing atom bombs. Tehran says its nuclear program is for purely peaceful ends, such as electricity generation.

Iran held talks with the U.N. watchdog International Atomic Energy Agency (IAEA) this month to clear up outstanding questions about its nuclear activity and improve IAEA inspectors’ access to its enrichment plant.

This, say some European diplomats, has prompted the six big powers working on the issue — the United States, Russia, China, Britain, France and Germany — to quietly put off until September efforts to toughen existing sanctions, in hopes Iran’s improved cooperation with the IAEA may defuse the standoff.

Brown said he believed the current sanctions were having an effect, but he thought there would still be a third resolution.

“There will probably be a third resolution in relation to Iran soon … I appeal to the Iranian authorities to understand the feelings that other countries have about the development of a nuclear weapons program,” he said.

French Foreign Ministry deputy spokesman Denis Simonneau told an online briefing it was necessary to maintain “a message of firmness” until Iran suspended sensitive activities.

“This new (U.N. sanctions) resolution, which we would like to be firm, should clearly indicate to Iran that its obstinacy is leading to its increased isolation, which is bad for its economy, its population and its openness to the world.”