Claims that the first shots in a new Gulf War have already been fired have been denied by Defence Secretary Geoff Hoon.
The no-fly zone policy has shifted, say Pentagon officials
Senior officials at the Pentagon say there has been a shift in strategy in no-fly zones in Iraq, with strikes intensified in what is seen as clearing the way for war.
Pressed about the reports in the House of Commons, Mr Hoon insisted the way the zones were being patrolled had not changed.
Iraqi claims that six civilians were killed and 15 injured in an Allied bombing raid on the city of Basra have now been disputed by the Ministry of Defence (MoD).
Officials said a "battle damage assessment" about Sunday's overnight no-fly zone attack showed there was no evidence anybody was killed or injured.
The allied planes targeted air defence targets in response to anti-aircraft fire from the ground, said the MoD, pointing to similar previous "unreliable" Iraqi claims.
Over the weekend Iraq began to destroy missiles banned by the United Nations since the end of the Gulf War - but that was dismissed by the US and UK as more deception.
On Monday, Mr Hoon told MPs he had given permission for the 14 US Air Force B-52 bombers to be stationed at RAF Fairford in Gloucestershire.
The first of the long-range aircraft arrived at the base on Monday, with Mr Hoon also announcing there were now 30,000 UK troops in the Gulf region.
The move was part of "contingency preparations" and no decision on military action had been made, the defence secretary told MPs.
In Iraq, new targets in the no-fly zones hit in recent days have included surface-to-surface missile systems and multiple launch rockets that could be used by Iraq against ground troops or neighbouring nations such as Kuwait.
Conservative shadow defence spokesman Bernard Jenkin challenged ministers to be "honest and open" about the change.
Mr Jenkin asked: "While we still hope diplomacy will avoid the need for the last resort of
war, haven't we already seen the opening shots of the second Gulf war?"
Mr Hoon insisted there had been no "substantial change" in the way the no-fly zones were patrolled.
"Clearly those forces have always been entitled to deal with threats that might arise," said Mr Hoon.
That was true whether they were direct threats from aircraft above the no-fly zones or threats to troops on the ground in areas like Kuwait, said Mr Hoon.
He did say Allied planes were mounting more frequent patrols of the no-fly zones "in response to efforts to attack them".
Liberal Democrat defence spokesman Paul Keetch said Mr Hoon's denial of a change in patrols - despite the Pentagon briefings - raised suspicions.
Mr Keetch said: "The no fly zones have no official sanction from the United Nations and it is imperative that they are not abused, especially when the UN Inspectors are hard at work in Iraq."
Anti-war Labour MPs are angry, with Alice Mahon suggesting last week's Iraq debate was a mockery because war was beginning "through the back door".
'No security checks'
Some of the intensification of strikes is down to repeat attacks on sites repaired by the Iraqis.
Iraqi aircraft were banned from the two zones in the aftermath of the Gulf War as part of the US policy of containing Saddam Hussein.
The UK Government also said on Monday it had not been able to carry out security checks on crews of merchant ships chartered to carry military equipment to the Gulf.
Defence Minister Lord Bach said the short notice charters made such checks impractical.
The Washington Post quotes US officials in Kuwait as saying the American 15th Marine Expeditionary Unit is likely to be assigned to a British command in the event of a war.
The move, unseen since Montgomery commanded American troops in World War II, is said to be a gesture rewarding Tony Blair for his support.