Baghdad, Iraq ? Iraqi forces for the first time took over security responsibility for an entire province Thursday, a milestone in the American plan to transfer control of the entire country by the end of next year.

British Maj. Gen. John Cooper signed the document turning over responsibility for Muthanna province, a relatively peaceful, sparsely populated Shiite province that had been under British and Australian control.

“It is a great national day that will be registered in the history of Iraq,” Prime Minister Nouri al-Maliki said in a ceremony in the provincial capital of Samawah. “This step will bring happiness to all Iraqis.”

The strategy of transferring all 18 provinces to Iraqi control depends on the capability of Iraq’s newly trained police and army to maintain order against threats by Sunni insurgents and sectarian militias. During the handover ceremony, al-Maliki warned that “the terrorists” were bent on upsetting the process and destroying Iraq’s national unity.

“They will spare no effort to destroy this step and ensure that no further steps are taken,” al-Maliki said. “But, with solidarity and patience, you will cut off the hands that want to sabotage this region.”

Iraqi forces marched in formation past the prime minister and other dignitaries at a stadium in Samawah, a city about 230 miles southeast of Baghdad. Local tribal leaders wearing traditional Arab headdresses and robes then approached the dignitaries’ tent, waving rifles and chanting, “We are ready to die defending this soil.”

“We were and are helping to build a strong, peaceful democratic society in Iraq,” Cooper said. “Today is an important step in that process.”

Only about 700 British and Australian troops were stationed in Muthanna, along with about 600 Japanese soldiers on a separate humanitarian mission. The Japanese troops are in the process of leaving the country, while the British and Australians will redeploy elsewhere in southern Iraq to stand in reserve in case the Iraqis need help with security.

Nevertheless, the handover marked a major step in the transformation of Iraq since the 2003 U.S.-led invasion and the collapse of Saddam Hussein’s regime.

Coalition forces are expected to hand over responsibility soon in other quiet southern provinces. If all goes well, the U.S.-led coalition plans to transfer responsibility for the 17 other provinces by the end of next year.

U.S. and other international troops would then step back, allowing the Iraqis to run security while staying in reserve in case of a crisis. That would be followed by a third stage in which U.S. troops would leave Iraq.

National security adviser Mouwafak al-Rubaie said he was confident the Iraqis could meet the challenge in Muthanna, where he acknowledged the threat of violence was low.