"After receiving the news, Iraqi police, army and US forces arrived and defused several unexploded bombs on the bridge."
Several nearby villages were raided after the bombing and 15 Iraqis were taken into custody for questioning.
The half-kilometre long bridge crosses the al-Adhaim river, a seasonal waterway that flows out of the remote Himreen hills, about 150km north of the capital.
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"Al-Qaeda militants train throughout the area and it's where they retreat to after doing operations in Baghdad, Balad, Kirkuk and Tikrit," Sheikh Fayez Abdallah al-Hayazi, a local tribal leader, said.
"Himreen's hills have become a base for militants, because Iraqi forces have been unable to control the area - everyone here is either loyal to al-Qaeda or live in fear of them."
In April, two bridges crossing the Tigris in Baghdad were hit by bombs, one of them, the Sarafiyah bridge, was totally destroyed.
Abbas Hilmi, who runs a taxi service between Kirkuk and Baghdad, said: "I left at dawn today with passengers and tried to cross the bridge but instead found hundreds of cars stranded and the bridge badly damaged."
"It is a miserable situation for us, it cuts the main road and our main source of income."
Meanwhile, a senior al-Qaeda commander in Falluja was shot dead by unknown men, police said.
Colonel Tareq al-Dulaimi, a senior police intelligence officer with close ties to Anbar province's tribal coalition, confirmed reports that Muwaffaq al-Jugheifi had been killed but did not identify the attackers.
|Al-Maliki, right, urged Turkey |
not to enter Iraq [EPA]
The attack comes just a day after Anbar's tribal forces announced they had sent 50 plain clothes secret police into the west Baghdad neighbourhood of Amiriyah to kill al-Qaeda members battling with rival groups.
An interior ministry official, who did not want to be named because he was not authorised to release the figures, said 1,944 civilians were killed in May, a 29 per cent rise over April.
At least 174 soldiers and policemen were killed in the same period.
The death toll was based on statistics compiled by Iraq's ministries of interior, defence and health on the number of people killed and wounded in attacks in Iraq.
A sharp rise in the number of sectarian murders in Baghdad was reported after three months of decline.
Police, who reported fewer than 10 sectarian murders a day in the first weeks of the security crackdown which began in February, are now typically reporting 30 or more.
Plea to Turkey
In another development, in Erbil, the capital of Iraq's autonomous Kurdistan region, Nuri al-Maliki, the Iraqi prime minister, and Masoud Barzani, president of Kurdistan, urged Turkey on Saturday not to send troops into the region to crush Kurdish separatists believed to be hiding there.
Al-Maliki said: "If there are problems then we shouldn't resort to threats, power and weapons because this worsens the problems.
"We don't want to harm neighbouring countries, but we also don't want neighbouring countries to interfere with military raids."
Recent troop movements on Turkey's southeastern border have prompted speculation about possible military action.