Iraq's top security chiefs said Sunday that the U.S. military had warned them in advance about an imminent attack but the tip came too late to act on before last week's deadly Baghdad bombings against government sites.
An Interior Ministry official, meanwhile, said 13 al-Qaida-linked suspects have been detained in connection with last week's bombings, the third of their kind since August.
At least 127 people were killed and more than 500 wounded in the bombings.
The disclosure of the U.S. tip and the announcement on the arrests came on the third day of a grilling by Iraq's parliament of government officials on the security breaches that allowed Tuesday's attacks to take place in some of the most heavily protected sections of the Iraqi capital.
Trying to contain some of the political fallout, Iraq's interior minister hinted during a parliamentary session of the arrests. "There are 13 coffins waiting for criminals implicated in Tuesday attacks, and those criminals will be tried and convicted," the minister, Jawad al-Bolani, told lawmakers.
He did not elaborate, but an official at his office later said al-Bolani was referring to the 13 arrests of al-Qaida-linked insurgents whom he said helped mastermind the bombings.
They are the first arrests confirmed after Tuesday's blasts, the official said.
The official spoke on condition of anonymity because he was not authorized to speak to media.
The U.S. military did not immediately confirm the arrests.
News of the arrests followed the announcement in parliament earlier Sunday by the former top military commander for Baghdad that an unspecified number of street-level security officials have been detained for alleged negligence that allowed the Tuesday bombings to take place.
Lt. Gen. Abboud Qanbar did not give more details, but authorities had taken similar measures following bombings on Aug. 18 and Oct. 25 which left at least 250 people dead.
Baghdad's security command was warned by the U.S. military that insurgents would carry out three attacks, including one in or near the Green Zone, Qanbar said.
Prime Minister Nouri al-Maliki replaced Qanbar as Baghdad's military commander after angry lawmakers demanded answers about the security breaches that allowed last Tuesday's suicide car bomb attacks.