BAGHDAD, Iraq (AP) - Iraq stood on the verge of its first free election in a half-century Saturday, its borders and bridges locked down, its hopes on the line. The government urged Iraqis to vote despite their fears of violence, even as insurgents rocketed the U.S. Embassy in Baghdad, killing two Americans.

Mortar fire boomed across Baghdad as the world awaited a vote that will echo from militant Islamic Web sites in the Mideast to the halls of the White House. A suicide bomber killed eight people in a Kurdish city near the Iranian border and insurgents blasted polling stations in eight cities.

Iraqi officials have predicted that up to eight million of 14 million voters will turn out for Sunday's election to choose a National Assembly and governing councils in the 18 provinces. Voters in the Kurdish-run north also will select a regional parliament.

But turnout is uncertain, especially in the Sunni Arab areas of central, northern and western Iraq where the insurgency is most deadly. About 300,000 Iraqi and American troops are on the streets and on standby to protect voters.

U.S. tanks and armored vehicles blocked roads and bridges to prevent insurgent movements. Iraqi National Guardsmen, wearing black ski masks to hide their faces, roamed through the capital in SUVs and pickup trucks, machine guns mounted. Police and Iraqi soldiers set up checkpoints and randomly searched cars.

As thousands of ballots arrived at 5,200 polling stations, government spokesman Thaer al-Naqeeb warned Iraqis to expect ''sabotage operations'' carried out by ''the enemies of Iraq.''

But he encouraged Iraqis ''to overcome their fear'' and turn out at polling station. ''It is important. It will preserve the integrity of Iraq,'' he said. ''If you vote … the terrorists will be defeated.''

President Ghazi al-Yawer, a Sunni Arab running for a National Assembly seat, expressed hope that turnout will be high.'' But he acknowledged many Iraqis would probably stay away ''because of the security situation.''

Despite the lockdown - and a nighttime curfew - guerrillas hit the U.S. Embassy compound in Baghdad's heavily fortified Green Zone with a rocket Saturday evening, killing a Defense Department civilian and a Navy sailor and wounding four other Americans, U.S. officials said. Another American soldier was killed by a roadside bomb in Baghdad. More than 40 American troops have been killed in the past three days.