"Individuals coming into Iraq from other countries for the purpose of endangering Iraqi civilians and disrupting security won't be tolerated."
In January, US officials said at least 170 US soldiers had been killed by EFPs since 2004.
The arrests in Sadr City came as the US military said it would continue building a concrete wall around Adhamiyah, a mainly Sunni district of Baghdad.
Colonel Don Farris, of the US army, said on Thursday that after briefly halting construction of the barrier, the Iraqi government had ordered the building of the wall to continue.
|US officers said the Iraqi government ordered|
the Adhamiyah wall work to continue [AFP]
He said: "We were asked to stop placing the barriers."
"Since then, it has been communicated to me through the chain of command that the prime minister and Iraqi security officials have authorised work to continue."
Farris said that the intention of the wall was still to stop vehicle movement into and out of the area, rather than to prevent the passage of people on foot.
He said: "It's not a wall - if you will - the intent is that there's no limitation of pedestrian traffic."
The construction of the wall in Baghdad may help to quell the city's violence, but bloodshed has continued around the country.
Munzir Baig, Muscat, Oman
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In Falluja, three US marines were killed in combat in the western province of Anbar on Thursday, the US military said.
Three other people were killed when they shot at a house belonging to a guard of MP Ezat Shahbandar from the Iraqi National List, a secular political bloc headed by Iyad Allawi, the former prime minister.
The attack took place in Mussayab, 60km south of Baghdad, police said on Friday.
In southern Iraq, a detainee died at Camp Bucca, a US military detention centre, after he was apparently assaulted by other prisoners, the US military said. The case was being investigated.
Meanwhile, in Washington, George Bush, the US president, has renewed his vow to veto a bill to withdraw US troops from Iraq and pledged to strike down any subsequent attempt by the Democratic-led Congress to set a deadline for a pullout.
"If the Congress wants to test my will as to whether or not I'll accept the timetable for withdrawal, I won't accept one," he told a news conference at his retreat in Camp David, Maryland, alongside Shinzo Abe, the Japanese prime minister, on Friday.
"So if they want to try again that which I have said was unacceptable, then of course I'll veto it."