Six US B-52 bombers landed in England yesterday and the British Foreign Secretary, Mr Robin Cook, said the cabinet would hold an emergency meeting today to discuss the Kosovo crisis.
The US Defence Secretary, Mr William Cohen, ordered the B-52s to Britain in readiness for possible NATO air strikes against Yugoslavia if it fails to heed UN demands to pull out of Kosovo.
"This is not a token gesture," the British Defence Secretary, Mr George Robertson, said before the bombers landed at Fairford air base in Gloucestershire. "There will be a phased series of air attacks on the Yugoslav military force if he [Yugoslav President Milosevic] does not comply with the will of the world," he added.
The B-52s landed at Fairford under partly cloudy skies about 15 minutes apart, starting a little before midday. They had left Barksdale Air Force Base in Louisiana on Saturday evening.
Mr Cook said a NATO session today was expected to order the alliance's military to be ready for strikes. He said he would then fly to Brussels tomorrow to meet the NATO Secretary General, Mr Javier Solana.
NATO was pursuing a twin-track strategy, Mr Cook said. "We are first of all making sure that we are ready to strike, we have the will to strike and the capacity to do so and at the same time we are using that preparation time to make sure that diplomacy backed by the threat of force is put to President Milosevic."
Maj Robyn Grantham of the US Air Force said at Fairford that while the B-52s could carry a number of different weapons, "I understand they are looking more at the conventional air-launched cruise missiles" in preparation for action in Yugoslavia.
Meanwhile, in northern Italy yesterday, A-10 Thunderbolt II jet fighters touched down.
The six aircraft arrived from Germany, where the US Air Force's 52nd fighter wing is based. They each carry a 30 mm Gatling gun that fires bullets the size of soda cans for penetrating tank armour or ripping up an airport runway.
Britain has already sent four Harrier ground attack jets to join four others based at Gioa del Colle in southern Italy.
Many of the US ground-based aircraft that may be involved in an eventual attack on Yugoslavia are already based in Italy, most of them at Aviano, a sprawling base north of Venice.
These include Canadian F-18s and US F-16s as well as AWACS early warning planes and airborne tankers. Some US aircraft are also based at the Villafranca base near Verona.
NATO can also attack Yugoslav targets from ships in the Mediterranean.
The Eisenhower battle group is now in the central Mediterranean simultaneously taking part in NATO's Dynamic Mix exercises and preparing for possible orders to strike Yugoslav targets.
The USS Eisenhower, an aircraft carrier, is home to F/A Hornet attack jets, F-14 Tomcat attack jets, radar-jamming EA-6B prowlers, E-2 Hawkeye tactical warning and control aircraft, and S-3 Vikings used for anti-submarine warfare and sea surveillance.
One of the ships clustered around the Eisenhower is the USS Anzio, a guided missile cruiser that carries Tomahawk land attack cruise missiles (TLAM).
It is likely that if NATO planners decide to use so-called "smart bombs" such as the Tomahawk in any strike, they will be fired from the Anzio.
The missiles, which were used extensively in the Gulf war, have a range of about 1,120 km (700 miles).
Before the Italian government collapse last Friday, communists supporting Prime Minister Romano Prodi's coalition said they would be opposed to the use of US bases without a clear UN resolution sanctioning strikes. But political commentators say now that Prodi is merely a caretaker prime minister he can give the go-ahead for use of the bases without worrying about risking his governing majority.