US forces in Iraq have launched a major security offensive around Baghdad.

Troops would enter "key areas" around the Iraqi capital used by insurgents to launch car bombings, said the commander of US forces, General David Petraeus.

US Defense Secretary Robert Gates has met top US military leaders in Baghdad to assess a security surge aimed at bringing Iraq under control.

He also met Iraqi Prime Minister Nouri Maliki, who said his government would rebuild a bombed shrine with UN help.

The meetings came as the US military announced it had found the identity cards of two US soldiers who have been missing for nearly a month.

The cards belonged to Specialist Alex Jimenez and Private Bryon Fouty, who were abducted with a third soldier, Private First Class Joseph Anzack Jr, south of Baghdad on May 12. The body of Pte Anzack has since been found.

The Islamic State of Iraq, an al-Qaeda-linked group, released a videotape earlier in June in which it said it had killed all three soldiers. US forces are still looking for Spec Jimenez and Pte Fouty.

Shrine repairs

During his meeting with Mr Gates, Mr Maliki said his government had "signed a contract with Unesco to immediately reconstruct" the al-Askari shrine.

The two minarets of the shrine, one of the holiest sites in Shia Islam, were destroyed in a bombing by suspected Sunni militants on Wednesday.

The shrine's golden dome was destroyed in an earlier attack in February 2006.

Baghdad offensive

The security crackdown around Baghdad had begun in the last 24 hours, Gen Petraeus said.

"For the first time we are really going to a couple of the key areas in the belts from which al-Qaeda has sallied forth with car bombs, additional fighters and so forth," he said.

With the US troop deployment in Iraq reaching a peak of 160,000, Gen Petraeus said the job of US and Iraqi forces was now "to do everything that we can with the additional forces that we have".

Mr Gates arrived in Baghdad as thousands of US and Iraqi troops enforced a curfew aimed at preventing the same level of violence seen after militants blew up the mosque's golden dome last year.

Speaking to reporters on Friday, Mr Gates said he had come to reinforce the message to Iraqi leaders that the "surge" was buying them time to pursue national reconciliation and that Washington wanted to see greater efforts.

"Frankly, we're disappointed with the progress so far, and hope that this most recent bombing by al-Qaeda won't further disrupt or delay the process," he said.

The BBC's Jim Muir in Baghdad says the politicians in the US are hoping to have something tangible to point to in July, when funding measures go before Congress, and even more by September, when political and military assessments of the surge and the overall situation in Iraq are due.

While the clock in Washington is running fast, that is not the case here, BBC correspondent says.

Several important pieces of legislation which are seen as vital to national reconciliation, including a new oil law, have yet to be passed by parliament.

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US troops in Iraq