“There can be little doubt that their destabilising foreign policies are a threat to the interests of the United States, to the interests of every country in the Middle East, and to the interests of all countries within the range of the ballistic missiles Iran is developing,”  Gates told delegates attending a conference on regional security in the Bahraini capital, Manama.

He claimed that Iran was also “funding and training” militias in Iraq and supporting what he called “terrorist organisations” such as Lebanon’s Shiite movement Hezbollah and the Palestinian Hamas.

Iran has consistently denied funding and training militias in Iraq.

Tehran charged

Gates charged that Tehran was developing “medium-range ballistic missiles that are not particularly cost-effective unless equipped with warheads carrying weapons of mass destruction.”

His accusations came five days after the publication of the US National Intelligence Estimate (NIE), which said that Iran halted a secret nuclear weapons programme four years ago -- a conclusion at odds with Washington's stance and accusations of recent years.

Gates conceded the timing of the report was not ideal. “The estimate fairly has come at a wrong time, it has annoyed a number of our good friends and confused a number of people,” he told delegates.

Suspicions about Iran's nuclear activities, which have particularly alarmed America's key regional ally, Israel, have been a key driver behind the tough US approach towards Tehran and its determined pursuit of sanctions against the Islamic republic.

“The US and the international community must continue -- and intensify -- our economic, financial and diplomatic pressures in Iran,” Gates maintained, adding that the US was seeking to forge more ways of applying pressure on Tehran.