US Secretary of State Colin Powell has warned of more violence in Iraq in the run up to the country's elections at the end of the month.
US and Iraqi forces continue to come under attack
He spoke after at least 23 people were killed in a suicide car bomb attack on a bus carrying Iraqi soldiers.
The killings happened outside an American military base at Balad, 80km (50 miles) north of Baghdad.
Mr Powell said that such attacks would not delay the elections, due to be held on 30 January.
"Poll workers are out working. While we see these
terrible scenes on television of Iraqi policemen losing
their lives, citizens losing their lives, citizens are also
coming out to register. They want to have an election," he said.
Packed with explosives
He also said a stronger national Iraqi security force was needed in the future.
"It has to get larger and it has to get more competent. It has
to get more equipment. It has to be trained. It has to gain
experience," he said.
In Sunday's attack in Balad, at least one suicide bomber in a car laden with explosives crashed into
the path of the bus.
The explosion happened in the area known as the Sunni Triangle, which has been the scene of repeated violence.
The BBC's Jim Muir in Baghdad says it was one of the most deadly of a recent spate of attacks, which have targeted both Iraqi and US forces in the run-up to elections.
In another incident, three Iraqi policemen were shot dead while on patrol in the city of Samarra.