U.S. military leaders are repeating claims that an elite Iranian military force supplied Iraqi insurgents with weapons and explosives.  But the Pentagon's chief civilian leader and top military officer said they do not know who in the Iranian government is involved. VOA's Jim Fry reports.

Iraqi soldiers have closed the Iranian border at Basra as part of a new effort to halt any Iranian weapons from getting into Iraq.  Media reports have raised questions about who U.S. officials believe is responsible.

At the Pentagon Thursday, Defense Secretary Robert Gates and Joint Chiefs Chairman General Peter Pace met with reporters to clarify.

Pace said it is important to distinguish between intelligence assessments and facts: "We know that there are explosives and weapons being used inside Iraq that were manufactured in Iran."

U.S. military officials said so Sunday (February 11th) in Iraq. They displayed what they said was proof that Iranian-made roadside bombs were being used against American forces.

A briefer claimed the highest levels of Iranian government were involved.  ?The assessments were based on those facts,? said General Pace. ?The assessment by that individual is what he said."

But Pace and Gates did not confirm that assessment: "Whether or not more senior political leaders in Iran know about it, we do not know.  And frankly, for me, either way it is a worry."

A reporter asked, "Given the increasing national skepticism over intelligence claims made by the administration, why should the American public now believe the links now drawn between Iran and terror groups in Iraq?"

To which the defense secretary replied, "I think that that evidence speaks for itself.  And I hope that the people will see that evidence in that respect.  We are not -- for the umpteenth time -- not looking for an excuse to go to war with Iran.  We are not planning a war with Iran.  What we are trying to do is -- inside Iraq -- disrupt the networks that put these weapons in the hands of those who kill our troops."

Meanwhile in Baghdad, U.S. and Iraqi forces are stepping up joint operations as part of a security crackdown.  Iraqis set up new checkpoints and soldiers conducted searches at multiple locations around the city. Despite the clampdown, there were more car bomb attacks and deaths in the capital.