Most of the six blasts occurred in Baghdad, reinforcing US military warnings that extremists remain capable of launching attacks in the capital despite an overall improvement in security.

The attacks took place on the eve of the US presidential election between Sen. Barack Obama and Sen. John McCain, who hold widely differing views on the war in Iraq.

Six people died and 21 others, including 10 policemen and two women, were wounded when a pair of bombs - one of them hidden in a trashcan - exploded in Tahariyat square in the Karradah district of central Baghdad during the morning rush hour.

US strategy in Iraq may change depending on the outcome of Tuesday's presidential contest.

Obama opposed the Iraq invasion of 2003 and has called for a complete withdrawal of combat troops in 16 months, while McCain supported the decision to go to war and opposes scheduling a troop withdrawal.

The US and Iraq are negotiating a new security agreement which would end the US military presence by 2012 and give Iraqis a greater role in managing combat operations.