London: Britain's armed forces are stepping up contingency planning for potential military action against Iran, amid mounting concern about Tehran's nuclear enrichment programme, a media report said on Thursday.

The Ministry of Defence (MoD) believed the US may decide to fast-forward plans for targeted missile strikes at some key Iranian facilities.

The Guardian daily quoting British officials said that if Washington presses ahead it will seek, and receive, UK military help for any mission, despite some deep reservations within the coalition government.

The British military planners of a potential attack are examining where best to deploy Royal Navy ships and submarines equipped with Tomahawk cruise missiles over the coming months as part of what would be an air and sea campaign, the report said.

The US would ask permission to launch attacks from Diego Garcia, the British Indian Ocean territory, which the Americans have used previously for conflicts in the Middle East.

US officials are likely to seize on next week's report from the International Atomic Energy Agency (IAEA), which is expected to provide fresh evidence of a possible nuclear weapons programme in Iran.

Quoting Whitehall officials, the paper said Iran has proved "surprisingly resilient" in the face of sanctions, and sophisticated attempts by the west to cripple its nuclear enrichment programme had been less successful than first thought.

Official now believe Iran has restored all the capacity it lost in a sophisticated cyber attack last year.