The alliance sent 68 combat aircraft backed by 17 support planes for air exercises over Macedonia and Albania, a signal of its presence in the region that was intended to deter President Slobodan Milosevic of Serbia from carrying out any further attacks in the province of Kosovo. None went within 15 miles of Yugoslav airspace, but the message was clear.
"We want to show that we are prepared to act if necessary in order to back up the international community to find a solution to this terrible problem of Kosovo," said the Nato Secretary-General, Javier Solana. "We are facing probably the last opportunity that president Slobodan Milosevic has to abide by international community recommendations in order to find a peaceful solution to the conflict," he told BBC radio.
As he spoke, British and French Jaguar ground-attack aircraft joined American F-16s, along with aircraft from Belgium, the Netherlands, Spain, Germany, Norway, Canada, Portugal, Greece, Turkey and Denmark. The presence of Greek aircraft, and the use of Greek bases, showed that in this confrontation Athens - which has remained loyal to Mr Milosevic in previous confrontations - is siding with its Nato allies.
Russia, which has also sided with Serbia in its clashes with the West, was more vocal in criticising the exercise. The Defence Minister, Igor Sergeyev, said that though he had attended meetings at Nato headquarters last week when the exercises were planned, they had been unexpected.
"We discussed the Kosovo problem. We all agreed that first of all it was necessary to resolve it with political measures. And as soon as I get back to Moscow, I find out that the exercises have begun. This was unexpected for me," he told the visiting US General, Hugh Shelton.
Russia recalled its senior military representative from Nato headquarters in protest, though this seemed to be more of a symbol than a real show of anger.
Mr Milosevic was expected in Moscow yesterday for talks with the Russian President Boris Yeltsin. Russia has agreed to try to persuade Mr Milosevic that the West is serious when it threatens further military action if the fighting in Kosovo is not brought to a close. The US President, Bill Clinton, was also due to speak to Mr Yeltsin last night.
At the EU summit in Cardiff yesterday, the Foreign Secretary, Robin Cook, said: "President Milosevic ought to look very closely at what is happening just over his border and remember that all options are open.
"He has got to stop the violence now and get back to the negotiating table."
Mr Solana said: "In view of the deteriorating situation on the ground, Nato just a few days ago took a number of far-reaching decisions.
"So, Nato is preparing to go further if required to halt the violence and protect the civilian populations."
But Nato believes that to go further, it will need a UN security Council resolution. Such a move was being discussed in New York yesterday, but Russia, as a permanent member of the Security Council, has a veto. So keeping Moscow happy will be vital if further action is to go ahead.
Nato's military planners were asked last week to prepare details of possible air and ground operations in the Balkans to support peace in Kosovo.
Kofi Annan, the UN Secretary-General, told reporters in Rome that Mr Yeltsin had promised to do everything that he could to persuade Mr Milosevic. "I think if we use diplomacy and force that threatens ... we should be able to succeed," he said.Reuse content