The event was attended by British foreign minister William Hague, German foreign minister Guido Westerwelle, Swedish foreign minister Carl Bildt and the high representative. The French and Italian foreign ministers were invited but could not make it.

A number of Arab diplomats also came. The list reportedly includes the secretary general of the Arab League, Amr Moussa, Egyptian foreign minister Nabil Elaraby, a delegate from Jordan, chief Palestinian negotiator Saeb Erekat and a delegate from Saudi Arabia.

None of the 'new' EU countries were asked along, including the Hungarian EU presidency and the incoming Polish presidency. There was no Israeli participation and no guests from staunchly pro-Israeli EU countries such as the Czech Republic and the Netherlands.

Spokespeople for Asselborn and Ashton declined to comment on the meeting, with Luxembourg saying only that it was "confidential."

The one guest who made a public remark was Bildt, who wrote in his blog that the event was "devoted [to] possibilities of a peace process in the Middle East".

An EU diplomat with knowledge of the matter told EUobserver the talks were aimed at finding a way to stop Palestinians from seeking UN recognition of statehood in September.

Ashton is concerned the move would expose a split in the union and damage relations between pro-Palestinian EU countries and the US. It could also ignite tensions in the region if the US uses its UN Security Council veto to block the initiative.

The high representative came to Luxembourg straight from an equally secretive meeting in Jerusalem with Israeli Prime Minister Benjamin Netanyahu and the international envoy to the Middle East, former UK leader Tony Blair.

But it is doubtful she brought Palestinian negotiator Saeb Erekat a strong incentive to abandon the UN plan.

"There is no indication that the Israelis are really interested in restarting the peace process at this stage," the EU diplomat said. "Bildt said the meeting was inconclusive, that it was premature to expect any solution at this stage," a Swedish diplomat noted.

Whatever was said at the dinner, Ashton's participation upset some EU countries.

"Member states meet in many formats, some of which are regional ones. But it raised eyebrows. If it's an ad hoc thing, it's OK. But if this kind of event becomes normal behaviour, then it could be a problem," a diplomat from one of the excluded EU countries said.

A diplomat from another excluded member state said it fortified Ashton's image of being pro-Palestinian rather than a neutral broker.

"She's already considered to be pro-Palestinian. She gives away gifts of toys made by children in Gaza. Of course, there's nothing wrong with that as such. But this kind of thing [the Senningen meeting] is not going to avoid a Kosovo moment in the EU. It won't help to smooth over divisions," the contact said, referring to the EU split over recognition of Kosovo sovereignty.