Iraq's Shi'ite prime minister asked parliament to fire his Sunni deputy, and security sources said an arrest warrant was issued for the Sunni vice president, straining the fragile sectarian coalition on the day the last American troops left.

The last convoy of U.S. soldiers rolled out of Iraq on Sunday ending nearly nine years of war but leaving behind a country in fear that a shaky peace between Shi'ites and Sunnis could collapse, reigniting sectarian slaughter.

Security sources and lawmakers said on Sunday an arrest warrant had been issued for Tareq al-Hashemi, one of Iraq's two vice presidents. They said Sunni and Shi'ite politicians had intervened to stop the arrest from being carried out.

Lawmakers also said on Sunday that a parliamentary official had received Prime Minister Nuri al-Maliki's request overnight for a vote of no confidence against Deputy Prime Minister Saleh al-Mutlaq.

Hashemi and Mutlaq, Iraq's two most-senior Sunni politicians, are leaders of the Iraqiya bloc, a secular group backed by many Sunnis, which joined Maliki's unity government only reluctantly and has long complained of being marginalised.

The Prime Minister told us that he cannot work with Mutlaq any more.... If this will affect the work and the performance of the cabinet then we will be with him, said Amir al-Kinani, a lawmaker from a Shi'ite bloc.

Iraqiya's parliamentary bloc suspended its participation in parliament on Saturday, accusing Maliki's Shi'ite-led government of concentrating power.

Iraqiya lawmaker Ahmed al-Alwani accused Maliki's authorities of carrying out political targetting - using the security forces and justice system against political opponents.

There must be a way of dealing with these issues, without replacing the celebration of the U.S. withdrawal with the politicisation of security matters to target political rivals, he told Reuters.

BODYGUARDS HELD

The security sources, who asked not to be identified, said the arrest warrant for Hashemi was issued after the vice president was linked to terrorist activities by four of his bodyguards, arrested on terrorism charges two weeks ago.

The existence of the arrest warrant for Hashemi could not be confirmed, and Iraqiya state television said Hashemi's office had issued a statement denying it. Reuters was not able to reach Hashemi for comment.

The large scale sectarian violence of 2006-07 has largely subsided, but tensions still simmer close to the surface, with many Sunnis feeling marginalised following the rise to power of majority Shi'ites after the ousting of Saddam Hussein.

In the last years of the U.S. presence, Washington worked hard to keep Sunnis inside the political process to prevent it from unravelling.

Iraq's power-sharing government splits the presidency, the prime minister's post, two vice presidencies and two deputy premierships among Shi'ite, Sunni and Kurdish blocs. But Sunni politicians complain they are kept out of decision making.

Iraqiya, led by former Prime Minister Iyad Allawi, a secular Shi'ite, won the largest number of seats in a March 2010 national election with the support of many Sunnis, but failed to muster a governing majority.

Instead, it joined a unity coalition headed by Maliki, winning posts such as the parliament speakership, vice presidency, and other ministerial positions, but it has since said it has been shunted aside by his lack of cooperation.

(Reporting by Suadad al-Salhy; Editing by Serena Chaudhry and Peter Graff)