Britain is sending more than 100 aircraft and 8,000 personnel to join the military buildup around Iraq.
The deployment in the coming weeks will include about 100 planes and 27 helicopters, with 8,100 support personnel.
It will be the biggest Royal Air Force mobilization since the 1991 Gulf war that drove Iraq out of Kuwait.
Britain has previously announced 35,000 troops are heading to the Persian Gulf region, along with the largest British naval task force in 20 years.
The defense secretary, Geoff Hoon, said Iraqi President Saddam Hussein must hurry up and comply with U.N. disarmament resolutions, if he wants to avoid a war.
"I have now announced the composition and deployment of forces from all three services," he said. "I recognize that this may tempt some people into speculation about the likelihood or timing of military action. It is still possible for Saddam Hussein to change his behavior, to cooperate actively with the weapons inspectors and to disarm by peaceful means. Time is running out. The Iraqi regime must decide whether it will comply with its obligations, or face the consequences."
On the diplomatic front, Britain hosted Iranian Foreign Minister Kamal Kharrazi. He told a news conference at the foreign office he worries about the consequences of war for the region.
"We are living in a very crucial time, and, naturally, we have to do our best to resolve this crisis, without necessity of using force," Mr. Kharrazi said. "We have, of course, our own concerns as neighboring countries to Iraq, because the outbreak of war would have its own repercussions on all neighboring countries in that region, including Iran. The simplest [obvious] one would be the influx of refugees to Iran."
British officials say the talks with Mr. Kharrazi focused on the need to ensure Iraq retains its sovereign territorial integrity in the event of a war. Also, they say, there were discussions of Britain's efforts to broker peace between Israel and the Palestinians.