A member of NATO since 2004, Bulgaria has planned a budget of 900 million euros ($1 billion) for the purchase of at least eight fighter aircraft.

It has received offers from the US for new Lockheed Martin F-16s and Boeing F-18s, from Sweden of new Gripen warplanes and from Italy for used Eurofighters.

The defence ministry is currently reviewing the offers and seeking improved proposals from the main bidders Lockheed Martin and Gripen.

"From what I have heard from the pilots, a new F-16 is a significantly better aircraft than all the rest that are on offer," Borisov told journalists in Brussels on Friday.

Borisov said he would not like to influence the work of the technical committee reviewing the offers, insisting that Bulgaria, which shares a Black Sea border with Russia and Ukraine, needed "the best aircraft as the situation in the region is getting more complicated".

Borisov and Defence Minister Krasimir Karakachanov are due to hold separate talks on Saturday with US Deputy Secretary of State John Sullivan, who arrived in Sofia Friday and is also lobbying for Lockheed Martin's offer.

"Lockheed Martin has made what I think is a very attractive proposal for the sale of fighter aircraft that other NATO allies have purchased that would make those aircraft, if purchased here, interoperable with those NATO partners," Sullivan said.

The US company on Friday signed a contract to sell 14 F-16 fighters to Slovakia for 1.58 billion euros.

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LOCKHEED MARTIN