BAGHDAD, Iraq - Sunni Muslim militants claimed responsibility today for the assassination of a community leader who was working to get out the vote on behalf of Iraq's top Shiite cleric, and three American troops were killed in persistent violence ahead of this month's elections.

The Sunni Muslim group of Ansar al-Islam said it targeted Sheik Mahmoud Finjan as a supporter of the Grand Ayatollah Ali al-Sistani, and "as a big supporter of the elections."

A separate ambush in Iraq's north killed three officials of a party representing Iraq's Kurds - like the Shiites, working aggressively for a high turnout in a vote expected to pry a large measure of power from Iraq's long-dominant Sunni minority.

U.N. Secretary-General Kofi Annan, meanwhile, said conditions for the Jan. 30 national elections were "far from ideal" and Iraqi officials should intensify efforts to make the balloting inclusive.

Finjan was one of many representatives of al-Sistani - Iraq's most influential Shiite cleric - working to get Iraq's suppressed Shiite Muslim majority to the polls.

Finjan was shot to death Wednesday as he headed home after evening prayers in a mosque at the town of Salman Pak southeast of Baghdad. Attackers also killed Finjan's son and four bodyguards.

The attacks were the latest blamed on Sunni extremists in what's expected to be an escalating campaign of violence aimed at intimidating would-be voters.

"We ... call upon all brother citizens not to participate in the elections because we are going to attack voting centers," Ansar al-Islam said in the statement claiming responsibility, renewing Sunni extremist demands for a boycott of the balloting. The message was posted on a Web site used by insurgents.

The U.S. military reported some of the latest violence today - the deaths of three U.S. troops in two provinces feared to be too violence-wracked for the vote.

Two Marines of the 1st Marine Expeditionary Force died in action Thursday in the western province of Anbar, the U.S. military said in a statement.

And a 1st Infantry Division soldier died while supporting Task Force Olympia operations around the volatile northern city of Mosul the same day, the military said. American forces gave no details.