US blames Lisbon Treaty for EU summit fiasco

"Up until recently, they [summits] would occur on six-month intervals, as I recall, with one meeting in Europe and one meeting here. And that was part of – the foundation of that was the rotating presidency within the EU. Now you have a new structure regarding not only the rotating EU presidency, you've got an EU Council president, you've got a European Commission president," he said.

"We are working through this just as Europeans themselves are working through this: When you have a future EU-US summit meeting, who will host it and where will it be held?" he added. "All of this is kind of being reassessed in light of architectural changes in Europe."

The Lisbon Treaty came into force on 1 December. It created the post of a new EU Council president and EU foreign relations chief in order to give the union a stronger voice abroad.

It kept the institution of the six-month rotating EU presidency as well, with the member state holding the chairmanship to do the bulk of behind-the-scenes policy work in Brussels.

The Spanish EU presidency is being closely watched to see how the EU manages the transition to the new power structure. The EU Council president has so far taken charge of summits in the EU capital. But Madrid was to share the limelight with a few top-level events at home.

The state department's Mr Crowley said the US and Spain have been in touch "directly" to discuss Mr Obama's decision after Madrid learned about it through the media on Monday.

"Obviously, there's been some disappointment expressed by the government of Spain, and we understand that and we'll be working with them on that," he said.

Spanish Prime Minister Jose Luis Zapatero and Mr Obama are both expected to attend the National Prayer Breakfast in Washington on Thursday. But no bilateral meeting has been announced so far.

The informal event sees some 3,500 celebrities, businessmen, politicians and religious leaders get together in the US capital each year. It is organised by the Fellowship Foundation, a Christian fundamentalist pressure group.

Mr Zapatero, a centre-left secularist, has taken flak for his trip in Spanish media, with the El Pais daily calling his decision to attend the prayer event "shocking."