Western news agencies were told by local people that the raid hit the Southern Oil Company - which supervises Iraq's oil exports under an oil-for-food deal with the United Nations.
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The US Central Command said its aircraft had attacked a communications facility after planes patrolling the northern no-fly zone had come under attack.
Coalition raids never targeted civilians, it said.
US and British war planes patrol two no-fly zones in Iraq, which were set up after the 1991 Gulf War to protect Kurds in the north and Shia Muslims in the south.
Iraq does not recognise the zones, describing them as "state terrorism and wanton aggression" in a letter from Foreign Minister Naji Sabri to the United Nations last week.
The US says Iraqi firing at Western jets is a direct violation of the UN resolution on disarming Iraq, but other Security Council member, including the UK, disagree.
Surprise inspection
The raid comes as United Nations weapons inspectors continue their hunt for Iraq's alleged stockpile of illegal weapons of mass destruction, conducting a surprise inspection at a helicopter base more than 30 kilometres (18 miles) north of Baghdad.
Weapons inspectors were investigating allegations that crop-spraying aircraft might have been converted to use biological or chemical weapons at the base at Khan Beni-Saad.
The BBC's Ben Brown says this was one of the most dramatic inspections so far.
The UN experts drove in at high speed through the gates of the base, and then blocked the entrance with one of their four-wheel drive land cruisers.
No-one was allowed in or out while they carried out their mission.
US delegation
The United States is sending a team of senior envoys to Europe on Sunday for consultations on Iraq.
The hawkish Deputy Defence Secretary Paul Wolfowitz will spend two days holding talks in London and at the Nato headquarters in Brussels, before travelling on to Turkey - whose airbases could play a key role in any attack against Iraq.
He will be accompanied by the State Department's Under Secretary for Political Affairs, Marc Grossman, who will go on to Cyprus, Greece, Germany, the Netherlands, France and Portugal after Mr Wolfowitz heads back to Washington on Tuesday.
Correspondents say the officials will be following up American requests to governments for military contributions in case of war, and seeking to build a more solid political coalition against Iraq.
The US has threatened to use force to disarm Iraq, which it alleges is in possession of weapons of mass destruction.