* Bomber kills lawmaker in Sunni heartland of Anbar
* No claims, but al Qaeda reviviing in province
* Attack may fuel tensions over mass Sunni protests
By Kamal Naama
FALLUJA, Iraq, Jan 15 (Reuters) - A suicide bomber killed an Iraqi Sunni Muslim lawmaker as he visited a construction site on Tuesday, threatening to deepen a crisis over Sunni protests against Prime Minister Nuri al-Maliki.
Posing as a worker, the attacker hugged Efan al-Esawi before detonating an explosive vest to kill the politician, who once campaigned against al Qaeda after the 2003 U.S.-led invasion, police and local officials said.
No one claimed responsibility for the bomb near Falluja, in western Anbar province. But insurgents may be seeking to stir tensions over Sunni protests at a time when sectarian violence is again on the rise since U.S. troops left in December 2011.
"One of the workers at the site went toward him, he thought he wanted something. The worker hugged him and then blew himself up," said Sadoun Ubaid, deputy head of Anbar provincial council.
"This man was targeted because he led the fight against al Qaeda. That is why they would target him," he said.
Esawi was one of the architects of Sahwa tribal resistance against al-Qaeda in Anbar's Sunni heartland that helped turn the tide of the war against insurgents battling U.S. troops at the height of the conflict.
Iraq's al-Qaeda wing, Islamic State of Iraq, has pledged to win back ground lost during the war and has been reinvigorated by Sunni Islamists fighting against President Bashar al-Assad in neighbouring Syria.
The Sunni protests have become a serious test for Shi'ite premier Maliki since they erupted in late December after authorities arrested the bodyguards of Finance Minister Rafaie al-Esawi, a Sunni Muslim, on terrorism charges.
Sunni leaders said those arrests were part of an extended campaign to unfairly target their minority sect by security forces. Many Sunnis feel they have been sidelined from power-sharing by the Shi'ite Muslim-led Baghdad government.
The unrest erupted as Syria's war, where mostly Sunni insurgents are battling Assad, an ally of Shi'ite Iran, is stirring regional tensions and testing Iraq's own fragile sectarian and ethnic balance.
Nearly 4,500 civilians were killed in insurgent-linked violence in Iraq in 2012, the first annual climb in the toll in three years, according to the rights group Iraq Body Count).
At least one big bombing took place each month in 2012, usually targeting security forces, government offices or Shi'ite Muslims. However, it has not reached the level of inter communal slaughter that followed the invasion which toppled former President Saddam Hussein.
Talks to end the protests have faltered, but lawmakers from Maliki's National Alliance Shi'ite coalition and Iraqiya are scheduled to meet on Wednesday afternoon, said Abbas al-Bayati, a member of the premier's political bloc.
Iraq's government said on Tuesday it had released more than 300 prisoners held under anti-terrorism laws as a goodwill gesture to try to appease demonstrators.
Sunni ranks are split over demands of the protests, with more hardline leaders calling for Maliki to step down and others seeking an amnesty law and modification of other legislation they say unfairly targets their community.