NATO officials say they have caught Iran red-handed, shipping heavy arms, C4 explosives and advanced roadside bombs to the Taliban for use against NATO forces, in what the officials say is a dramatic escalation of Iran's proxy war against the United States and Great Britain.

"It is inconceivable that it is anyone other than the Iranian government that's doing it," said former White House counterterrorism official Richard Clarke, an ABC News consultant.

Secretary of Defense Robert Gates stopped short earlier this week of blaming Iran, saying the U.S. did not have evidence "of the involvement of the Iranian government in support of the Taliban."

But an analysis by a senior coalition official, obtained by the Blotter on ABCNews.com, concludes there is clear evidence of Iran's involvement...