The leaders of France, Germany, Belgium and Luxembourg will attend the half-day summit, an initiative by Belgian Prime Minister Guy Verhofstadt.

"This summit is not directed against NATO or the Americans," said the Belgian leader.

British Prime Minister Tony Blair, whose country is one of the EU's biggest military powers, isssued a thinly-veiled warning to the participants.

"We won't accept, and neither will the rest of Europe, accept anything that either undermines NATO or conflicts with the basic principles of European defence we've set out."

During two hours of talks Tuesday morning, Verhofstadt will meet with German Chancellor Gerhard Schroeder, French President Jacques Chirac and Luxembourg Prime Minister Jean-Claude Juncker.

The four agree that the deep divisions opened up in Europe by the Iraq war underline the need for the EU to put flesh on the bones of its common foreign and security policy.

But the meeting has fueled talk of a two-speed EU, at a time when the bloc is struggling to build just the opposite, a Union increasingly united in areas other than purely economic affairs.

Critics claim the meeting, called by Verhofstadt shortly before the Iraq war erupted, is part of the Belgian leader's attempts to grandstand ahead of May 18 general elections. According to skeptics, Schroeder and Chirac agreed to atttend as a favour for Belgium's support during the Iraq crisis.

Britain, Italy, Spain and the Netherlands have all expressed reservations, and ensured that neither EU foreign policy chief Javier Solana nor the EU's current Greek presidency attend.

Among key issues at the mini-summit will be the creation of an EU armaments agency, an idea already backed by the convention on the future of Europe, the body sketching out the EU's future shape.

The four leaders will also discuss a "solidarity clause" to be included in a new EU constitution, guaranteeing support in the case of attacks on member states, as well as a proposal to create a European defence command headquarters outside Brussels.

French Foreign Minister Dominique de Villepin rebuffed suggestions that the meeting was a threat to NATO plans.

"Everything is being done to act in tight cooperation and in strict harmony with the Atlantic Alliance," he said.

But critics are watching the outcome of the meeting closely.

"If the embryo of an increased military cooperation were to develop in Brussels, I would regard it with a very critical eye," said Italian Foreign Minister Franco Frattini.

The summit, being held at the Belgian foreign ministry, was due to start around 10:00 am (0800 GMT). A press conference was scheduled in a Brussels hotel around 12:15 pm (1015 GMT).

SPACE.WIRE