Nine Iraqi police and a civilian have died in suicide bombings between Baghdad and Karbala, where Shias are attending a major religious festival.
Shia Muslim pilgrims have been entering the city by foot
The road is a popular route for Shia pilgrims travelling to the festival.
Thousands of Iraqi police and troops are in Karbala itself; while US-led coalition forces are stationed outside the city.
Over one million people are attending the festival, which marks the birth of a revered Shia leader, Imam Mehdi.
In other developments:
- The Iraqi government says a nephew of Saddam Hussein, Ayman Sabawi, has been sentenced to life in prison for funding Iraq's insurgency
- Two British Army tanks have been attacked and set on fire in Basra
- An Iraqi reporter working for the New York Times, Fakher Haider, has been found dead in Basra
- Police have reported finding more than 20 bodies on Sunday in the Tigris River at Balad, about 80km (50 miles) north of Baghdad
- Iraq's Finance Minister, Ali Allawi, tells the UK's Independent newspaper that large-scale corruption in Iraq's ministries, particularly the defence ministry, has led to the theft of more than $1bn.
An Iraqi defence ministry official said car bombers targeted two separate checkpoints maintained by Iraqi forces in the towns of Mahmudiya and Latifiya.
At least 12 people, including a number of Shia pilgrims, were wounded.
Both sites are on the route from Baghdad to Karbala.
Meanwhile the governor of Karbala has said that five people have been arrested for allegedly planning to attack the festival.
IMAM MEHDI BELIEFS
12th and final imam, or rightful successor to Prophet Muhammad
Born 868 and believed by certain Shias to be still alive and in hiding
He will reappear at Day of Judgement and pray in Jerusalem
The arrests come after police discovered explosives on the outskirts of the city - they said three of those arrested were foreigners.
A radical Shi'ite militia, the Mehdi army, said government pressure has forced it to withdraw forces it was deploying along the roads to Karbala.
Cars have been banned from the city, to reduce the risk of bombings, and pilgrims are being searched.
There are fears that Sunni insurgents who are trying to invoke civil war in the country may attack the festival, reports the BBC's Richard Galpin in Baghdad.
More than 260 people, mostly Shia Muslims, have been killed in an upsurge of violence that began on Wednesday.
The militant leader Abu Musab al-Zarqawi has reportedly called for war against Shias ahead of next month's referendum on a new Iraqi constitution.
The festival, which lasts several days, commemorates Imam Mehdi, the 12th and last Imam of the Shia Muslims.
Some pilgrims told the BBC they were more determined than ever to attend the festival following the reported threat by Zarqawi.
"He will not stop us from attending our rituals," said one man, as he set off from Baghdad.
Our correspondent reports that the authorities attempted to take maximum precautions ahead of the festival.
Hospitals in the area and in Baghdad were put on alert, and there was a campaign to get extra donations of blood from the population.