Polls are open in Iraq's parliamentary elections - a landmark ballot that voters hope will bring security and stability.

Shortly after voting began, a large explosion rocked Baghdad's heavily-fortified Green Zone, which contains the U.S. Embassy and Iraqi government offices. Early reports suggested the blast might have been from a mortar round.

Bombs also went off near polling stations in Ramadi, Tikrit and Mosul where one guard was killed.

Heavy security measures are in effect for the election, with tens of thousands of Iraqi troops and police on duty, backed by U.S.-led forces.

Millions of Iraqis will have to walk to their polling stations, since roads have been closed to traffic except vehicles with special permits.

Polling stations are to remain open for 10 hours (until 1400 UTC).

President Jalal Talabani urged all of Iraq's 15 million eligible voters to take part. He says a strong turnout will give a new government legitimacy and help defeat terrorists.

More than 6,000 candidates are competing for the 275 seats in the Iraqi parliament.

Some information for this report provided by AP, AFP and Reuters.