Diplomats said there was a sense of urgency about the London meeting, as fighting in Bosnia had increased in the past week and all but buried a four-month ceasefire due to expire on 1 May.
"We are at a very dangerous moment," the European Union's mediator, Lord Owen, said. "If we go into a major battle this summer, it will be very hard to keep the United Nations in Bosnia into the next winter."
The UN announcement on air strikes struck a different note from that sounded last year by Lieutenant-General Sir Michael Rose, the former UN commander in Bosnia. He at first countenanced Nato attacks on Bosnian Serb targets but ended up believing they undermined the UN's neutrality and jeopardised peace-keeping operations.
His successor, Lieutenant-General Rupert Smith, has made it known that a firmer approach is in the offing. Colum Murphy, a UN spokesman in Sarajevo, said: "There is some change. If necessary, this commander is going to take very forceful action."
The announcement may have been prompted by the fact that Bosnian Serb forces have shelled four UN "safe areas" - Sarajevo, Bihac, Tuzla and Gorazde - in the past week. The UN acknowledges that Muslim-led Bosnian government forces sometimes provoke such incidents by using "safe areas" as bases to attack Serb targets.
The latest fighting appears to have brought Muslim gains in the Tuzla and Travnik areas of northern and central Bosnia. Bosnian Serb officers say the Muslim-led forces, under-armed at the start of the war in 1992, now have more weapons and ammunition.
The Contact Group, exploiting a rift between President Slobodan Milosevic of Serbia and the Bosnian Serb leadership, hopes to persuade Mr Milosevic to recognise Bosnia in its pre-war borders, increasing pressure on the Bosnian Serbs to accept a peace settlement. France's Foreign Minister, Alain Jupp, expressed optimism last week that this was possible, saying: "Mutual recognition of Bosnia-Herzegovina and the Federal Republic of Yugoslavia [Serbia and Montenegro] is a goal within our reach and should come about before the end of April."
Mutual recognition between Serbia and Croatia seems a more remote prospect, because Mr Milosevic says the status of the Serb-held part of Croatia known as the Krajina is unresolved. The Western powers and Russia have proposed that Croatian Serbs receive broad autonomy, but it appears that Mr Milosevic is holding out for more in Croatia - possibly including a revision of borders in Serbia's favour - than in Bosnia.