Sofia (AFP) - Bulgaria's defense ministry asked the government on Friday to start direct talks with the United States on acquiring F-16 fighter jets to replace its ageing Soviet-built MiG-29 planes.

"The acquisition .... will raise the combat capabilities of Bulgaria's air force to a new level," the ministry said.

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

Lockheed Martin's initial offer however exceeded this sum.

"A lowering of the price, which according to them is doable, can only be achieved in direct government-to-government talks," Defence Minister Krasimir Karakachanov told a news conference.

The ministry also asked the government to seek parliament's approval for a higher budget in case a discount was not possible.

Conservative Prime Minister Boyko Borisov said last week that he favoured the F-16 fighters over the other offers, which include Boeing F-18s, Gripen fighters from Sweden and used Eurofighters from Italy.

Borisov discussed this with US Deputy Secretary of State John Sullivan, who visited Sofia last week and lobbied for Lockheed Martin's offer, as well as with US Secretary of State Mike Pompeo.

In an improved offer, Sweden's Gripen said last week it could supply 10 fighters for the same sum but defence ministry officials said that both the Swedish and Italian offers did not include costly weapons that had to be bought separately.