A car bomb in Iraq's holy city of Najaf has killed at least three people and wounded 50 on the eve of tense parliamentary elections, officials say.

The blast struck near the Imam Ali shrine, popular with Shia pilgrims from Iraq and Iran.

It came despite security being ramped up nationwide ahead of Sunday's polls.

Dozens have died as sectarian tensions mounted ahead of the elections, the second parliamentary poll since Saddam Hussein was ousted in 2003.

Friday was the last day of campaigning across the country.

The BBC's John Simpson in Baghdad says many people are nervous that Iraqi authorities are solely responsible for security ahead of the polls.

With 3,000 people a year being murdered in Baghdad alone, some say the security situation was better when it was under US-led control.