Wednesday, March 15 2006 19:42 Hrs (IST) - World Time -

Washington: US Defence Secretary Donald Rumsfeld acknowledged the United States cannot prove the Iranian government is behind the movement of Revolutionary Guard forces and bomb-making equipment into Iraq.

But he told sources "a reasonable man test would suggest that they are not freelancing and they are not pilgrims."

US leaders have stepped up attacks on Tehran in recent days as bursts of sectarian violence in neighbouring Iraq have raised fears of civil war.

President George W Bush on Monday accused Tehran of providing Shia militia with the means to build improvised explosive devices of increasing lethality.

And last week, Rumsfeld directly accused the Iranian government for the first time of sending Revolutionary Guards across the border into Iraq to make trouble.

But when asked at a Pentagon press conference whether he had proof that the Iranian government was directly involved, General Peter Pace, the chairman of the Joint Chiefs of Staff, said: "I do not, sir."

Elaborating on the answer, Rumsfeld said one cannot know if devices used in bombs are being brought in by the Iranian government "unless you physically see it coming in a government-sponsored vehicle or with government-sponsored troops."

"With respect to people, it's very difficult to tie a thread precisely to the government of Iran," he said.