* First ballot since US troops left at end of 2011
* Maliki's Shi'ite coalition already in strong position
* Sunni leadership sharply split over political future (Adds details from ground)
By Patrick Markey
BAGHDAD, April 20 (Reuters) - A dozen small bombs exploded and mortar rounds landed near polling centres in Iraq on Saturday, wounding at least four people during voting in the country's first provincial elections since the departure of U.S. troops.
Two mortar rounds injured three voters and a policeman at a school used as a voting centre in Latifiya, south of Baghdad, soon after the start of the ballot that will measure parties' political strength before parliamentary elections in 2014.
Attacks have surged since the start of the year with a local al-Qaeda wing and Sunni Islamists stepping up their campaign to undermine the Shi'ite-led government and stoke confrontation among the country's combustible sectarian and ethnic mix.
Small bombs exploded in Tuz Khurmato, Tikrit and Samarra in the north and six more mortar rounds landed in a town near the southern city of Hilla, without causing any injuries, said police.
Iraqi politics is deeply split along sectarian lines with Prime Minister Nuri al-Maliki's government mired in crisis over how to share power between majority Shi'ite Muslims, Sunnis and Kurds who run their own autonomous enclave.
For Maliki, a strong showing by his Shi'ite State of Law alliance may open the way for a shot at a third term in 2014 elections when he has hinted at plans to abandon Iraq's unwieldy power-sharing deal to form a majority government.
Sunni rivals, deeply divided over how to work with his government, and the premier's Shi'ite rivals, anti-U.S. cleric Moqtada al-Sadr and the ISCI movement, will look to chip away at Maliki's sway over provincial councils.
Security was tight across Iraq with more than 8,000 hopefuls running for nearly 450 seats on provincial councils which select local governors. More than a dozen candidates, mostly Sunnis, were killed during campaigning.
Early turnout at polling stations in Baghdad, and cities like Basra, Tikrit and Baquba appeared light, according to Reuters reporters.
Many Iraqis are frustrated with insecurity, unemployment, rife corruption and the lack of basic services a decade after the invasion that ousted Saddam Hussein and helped trigger sectarian bloodshed that killed tens of thousands in 2006-2007.
Attacks on a Sunni and a Shi'ite mosque on Friday killed at least eight. A suicide bomber killed 32 people in a blast at a popular cafe in a mostly Sunni neighbourhood in Baghdad a day before.
Since American troops left in December 2011, Iraqi politics has been paralyzed by infighting over power-sharing agreements with Maliki's rivals accusing the Shi'ite premier of consolidating power at the expense of Sunni and Kurdish partners.
"I took part in past elections, but all those we elected did nothing for the people," said Ali Hussein Sharqi, voting in the southern oil hub of Basra. "We want people who will offer jobs to the jobless."
Three provinces in Iraq's autonomous Kurdistan region, run by ethnic Kurds since 1991, and the ethnically mixed, disputed city of Kirkuk, will not be voting on Saturday.
Washington weighed into the election process, asking the government not to alienate Sunni voters after the Cabinet postponed voting in two mostly Sunni provinces because local officials warned they could not provide security there.
Since December, tens of thousands of Sunni Muslim protesters have taken to the streets each week to demonstrate against what they say is the marginalisation of their minority sect.
Election authorities say suspended voting in Anbar and Nineweh provinces may go ahead in a month.
But ten years after the invasion, many Iraqi Sunnis feel they have been sidelined by the country's majority Shi'ite leadership and discriminated against by Iraqi security forces and tough anti-terrorism laws.
"Suspending elections was the coup de grace for the demonstrations. We've as lost everything," said Maitham Jalal, a college student in Anbar province. "Elections are a legitimate right which was taken away by the government without any fear."
Sunni-backed Iraqiya block has struggled to stay united with its leadership split over how to manage relations with Maliki. Those divisions are likely to play out in the provincial election results.
"Overall the elections are likely to see Iraq stumble further along the trajectory on which is has already been headed for some time: to stratified, sectarian politics," Eurasia Group analyst Crispin Hawes wrote in a report. (Additional reporting by Ahmed Rasheed and Raheem Salman in Baghdad; Aref Mohammed in Basra; Editing by Stacey Joyce and Andrew Heavens)