BAGHDAD — Defense Secretary Leon Panetta said the U.S. would do “everything that is necessary” to go after Iranian weapons entering Iraq following a recent spike of deadly Shia militant attacks on U.S. troops — the second top U.S. defense official in three days to sound a strong warning to Tehran.

“I don’t want to get into particulars, but I do want to make it clear that we have the authority to defend our people,” he said Sunday in Afghanistan, before flying to Baghdad to continue his first tour of the war zones as secretary.

“We’re seeing more of those weapons going in from Iran, and they’ve really hurt us,” Panetta said, answering the first question asked, on Iran’s involvement in both countries, during an open session with troops at Camp Dwyer in Afghanistan.

Panetta told sailors and Marines that the U.S. is concerned that 15 American servicemembers were killed in Iraq in June, nine by Iranian-made rockets, known as improvised rocket-assisted munitions, or IRAMs.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, gave a similarly strong warning Thursday at the Pentagon, one day after two U.S. soldiers were killed by a roadside bomb at a checkpoint leading into heavily fortified Victory Base Complex, the Baghdad headquarters of U.S. Forces - Iraq.

“Iran is very directly supporting extremist Shia groups which are killing our troops,” Mullen said. “And there’s no reason, with some 46,000 troops that I have there now, for me to believe they’re going to stop that as our numbers come down.”

A senior defense official traveling with the secretary and speaking anonymously per Defense Department rules, said Friday that the U.S. expected Iran to try to “bloody our noses” during the withdrawal.

“They are clearly trying to create the impression that they’re driving us out,” the official added Sunday. “The Iranian Shia militants are clearly on the march.”

While Iraq has suffered constant attacks this year, the new aim at U.S. forces particularly troubles defense officials.

A bilateral security agreement signed by President George W. Bush requires nearly all U.S. forces to exit the country by Dec. 31. U.S. officials including President Barack Obama this year have asked Iraq to come up with a request to extend the American presence, reportedly with many as 10,000 troops.

But Iraqi leaders are embroiled in political divisions that have kept Prime Minister Nouri al-Maliki from appointing a defense minister and interior minister, who control the army and police. Without those key officials, Iraqi political leaders in negotiations Saturday about a possible troop request came out empty-handed, according to The Associated Press.

Panetta is scheduled to meet with al-Maliki and President Jalal Talabani, as well as U.S. officials and troops. He will not ask the Iraqis to let U.S. troops stay beyond the deadline or present any optional plans, aides say.

“I’ll encourage them to make a decision,” Panetta told reporters, in Afghanistan. Pressed, he would not say whether he believes U.S. troops should stay beyond 2011. “I think it’s really dependent on the Iraqis.”

Talabani said a decision will come within two weeks, several media outlets reported Sunday.

For now, Panetta said, the U.S. should partner with Iraqis to find the Iranian weapons in the country, in addition to diplomatic pressures on Tehran.

Besides Iran, U.S. officials are concerned about Iraq’;s ability to defend its borders and airspace if American troops pull out entirely. This year, Gen. Lloyd Austin, commanding general of U.S. Forces - Iraq, and others have said Iraq needs, at least, more training in combined arms, air defenses, and intelligence and logistics support.

Earlier Sunday, Panetta toured Camp Dwyer, dining with captains, visiting the 115th Combat Support Hospital and medevac helicopter crews, and walking in temperatures over 110 degrees through an area where Afghan soldiers were learning weapons training, how to drive, and how to detect and clear homemade bombs.

Brig. Gen. Lew Craparotta, commanding general of Task Force Leatherneck, and Col. Dave Furness, commanding officer of Regimental Combat Team-1, told reporters the combination of U.S. pressure on insurgents and supply chains, the growing and improving Afghan security forces, and the trust of locals is choking out insurgents in Marjah, Garmsir and Nawa districts.

But insurgents are still fighting to get back into many areas in the region, with deadly fire erupting daily in Sangin and further north.

“No, the war is certainly not over, here,” Craparotta said.

Yet, both commanders said in earnest they sense things are changing for the better since they arrived last August.

“He’s under pressure from a lot of fronts,” Furness said of insurgents. “I haven’t met an Afghan in a year that isn’t sick and tired of fighting.”

Later this year, 800 troops of the 3rd Battalion, 4th Marines will redeploy from this region without being replaced, in the first wave of Obama’s force drawdown. Craparotta will have to “backfill,” he said, other troops into those areas where they are still needed.

When asked how the region would cope with losing potentially more troops to the drawdown ordered back in Washington, Craparotta said, “We’ve got plenty of time to manage our forces.”

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