Erjavec told the parliamentary Foreign Policy Committee that Mussomeli had told him on Tuesday "that according to his information, Slovenia was not spied on," but that the ambassador would verify the information again.

The foreign minister also said that he had invited Mussomeli for the meeting and also met with him - he labelled this a regular procedure - updating a previous account from the ministry indicating that the Director for Bilateral Affairs Marjan Cencen hosted the meeting.

The minister told MPs that it was difficult to assess how the spying allegations would impact on EU-US relations and the talks on a free trade agreement between the sides since many details about the alleged operation were still unclear.

The issue will likely be on the agenda of upcoming meetings of EU foreign ministers, Erjavec announced.

His comments come a day after the Foreign Ministry said it had summoned Mussomeli for a meeting on the allegations that the US National Security Agency (NSA) was conducting spying operations at EU missions in the US and in countries of the EU.

The ministry said in a statement that Slovenia demanded explanations from Mussomeli on media reports suggesting that the NSA was spying on European missions in Washington, EU institutions and even on individual countries.

The US Embassy in Ljubljana confirmed on Tuesday the meeting at the Slovenian Foreign Ministry, labelling it "a useful exchange of views between allies and friends".

The meeting took place after German weekly Der Spiegel cited documents from ex-NSA contractor Edward Snowden in reporting on Saturday of a US spying operation targeting EU institutions, including the EU Mission in Washington and the EU Mission to the UN in New York.

This was followed on Monday by a story from Britain's The Guardian, which published a secret document from 2010 alleging that the NSA targetted 38 foreign missions in the US using sophisticated bugging and electronic surveillance technology.

The fresh allegations about NSA spying operations surfaced three weeks after Snowden leaked documents of a secret NSA electronic surveillance programme with which the US was monitoring internet communication around the world.