Meanwhile, on May 30, the autonomous northern Iraqi region of Kurdistan signed a security cooperation accord with the U.S.-led coalition.

The accord was signed by Kurdistan President Masoud Barzani and U.S. commanders in Irbil. The accord stipulated the handover of coalition security responsibility to the Kurdish regional government in the provinces of Dohuk, Irbil and Suleimaniya, Middle East Newsline reported.

Officials said the Bush administration has warned Turkey that an invasion of northern Iraq to uproot Kurdish insurgency strongholds would destabilize the region. They said the United States would instead encourage Iraq and the autonomous Kurdistan government to act against the Kurdish Workers Party.

At a news conference on Sunday in Singapore, Gates responded to reports of a Turkish military buildup along the Iraqi border. The Pentagon chief sounded sympathetic to Turkey's increasing concern over PKK infiltration.

"The Turks have a genuine concern with Kurdish terrorism that takes place on Turkish soil," Gates said. "So one can understand their frustration and unhappiness over this. Several hundred Turks lose their lives each year, and we have been working with the Turks to try to help them get control of this problem on Turkish soil."

Turkey was said to have amassed 60,000 troops along the Iraqi border. The Turkish military, saying it was awaiting an invasion order from the government, has also deployed at least 300 main battle tanks as well as attack helicopters and fixed-wing aircraft in the southeast.

Turkey has been concerned over the emerging authority of Kurdistan. The autonomous government has demanded responsibility to sign crude oil and natural gas contracts.

"Transferring the security operation does not imply that the province is moving towards secession or independence," Kurdistan Democratic Party secretary Fadil Merani said. The U.S. warning, voiced on June 2 by Secretary of State Condoleezza Rice, came amid an appeal by Iraqi Prime Minister Nouri Al Maliki. On June 2, Al Maliki said Baghdad would not allow Turkey to convert northern Iraq into a war zone.

"Our view is we would prefer to continue to work this problem with them to try and safeguard Turkey and would hope they not take unilateral military action across the border into Iraq," Gates said. Officials said the memorandum of understanding with Kurdistan took more than a year to draft. They said the more than 30-page agreement outlines the relationship between Kurdish security forces and the U.S.-led coalition.

The MoU also outlines the contribution of Kurdistan to the current coalition security operation in Baghdad. In addition, the agreement would establish a security coordination center in Irbil.

"The memorandum between the province and Americans also establishes a coordination center in Irbil linked to Baghdad and the coalition forces operation center," Kurdistan security forces spokesman Jabbar Al Yawar said. "In practical terms, the memo lifts security protection provided by American forces for Iraq Army and security services in Kurdistan."

The agreement marked the largest security handover by the U.S.-led coalition to Iraq in 2007. Kurdistan, deemed the quietest region in Iraq, has attracted foreign investment and oil projects.

But over the last three months, officials have warned of Iranian infiltration of Kurdistan. They said Iran has used Al Qaida-aligned insurgents and the Mahdi Army to intimidate Kurdish villages and authorities.

A U.S. official said the transfer means Kurdistan would oversee the Iraq Army and police, as well as other security forces. Maj. Gen. Kurt Cichowski, deputy chief of staff for strategy, cited the so-called "peshmerga," now known as the Kurdish Regional Guards.

Cichowski said the transfer was based on the achievement of four measures: regional security; Kurdish security capabilities; local governance capability; and the Kurdish-coalition relationship. He said Kurdistan, with modern hotels and international companies, has become prosperous in the post-Saddam Hussein era.

"There is a very important change in status," Cichowski said.