Iraq took full control of a province from foreign troops for the first time since the 2003 US-led invasion on Thursday, but clashes in Baghdad underlined the security challenges facing the new government.
Addressing a ceremony to mark the handover of southern Muthanna province from British-led troops to Iraqis, Iraq's prime minister warned that insurgents would try to stage attacks to mar a day "written with golden letters in Iraq's history".
"Terrorists who want to disrupt the handover of security and the success of the national unity government will not spare any effort to sabotage this step," Nuri al-Maliki said in the provincial capital Samawa, 270 km (168 miles) south of Baghdad.
"If this experience fails, this could lead to a big setback which could affect our efforts to control security," Maliki said of the handover, the first since the war toppled Saddam Hussein.
Though relatively calm compared to other regions in central and western Iraq where a Sunni Arab insurgency is raging and sectarian tensions run high, the handover of largely desert Muthanna marks a symbolic step in Maliki's efforts to win more autonomy from foreign troops.
It will also test Iraq's fledgling security forces, whose build-up is key to allow an eventual withdrawal of the roughly 140,000 foreign troops in Iraq. The Kurds have run three provinces in the north since 1991.
In a joint statement, the US ambassador Zalmay Khalilzad and the US commander in Iraq, General George Casey, hailed it as a milestone in Iraq's capability to govern and protect itself as a "sovereign nation" and said handovers in other provinces will take place as conditions are achieved.
"With this first transition of security responsibility, Muthanna demonstrates the progress Iraq is making toward self- governance," the statement said, adding that "Multi-National Forces will stand ready to provide assistance if needed".
But in more of the violence that has raised the spectre of civil war and exposed serious gaps in the month-old Baghdad security plan, clashes erupted between gunmen and Iraqi police in Ghazaliya, a Sunni neighbourhood in western Baghdad which has seen fierce fighting between Sunni and Shi'ite fighters.
The Association of Muslim Scholars, a leading Sunni religious group, said gunmen had attacked one its mosques in Ghazaliya. Police said two people were wounded in clashes.
Scores have been killed in recent sectarian violence and Maliki told parliament on Wednesday his national reconciliation plan offered Iraqis their last chance for peace.
Shi'ite militias loyal to anti-occupation cleric Moqtada al-Sadr are strong in Samawa and residents have complained of collusion between police and the militias, who have been accused by critics of sectarian attacks.
Britain's ambassador to Iraq, William Patey, acknowledged the province was not trouble-free but added: "That is not the standard we are setting. What country is trouble-free? "The question is are the local security forces capable of dealing with it," he told Reuters.