Lockheed Martin co, the United States’ largest weapons maker, has fielded interest from Croatia regarding the purchase of stealthy F-35 jets, a Lockheed executive said on Friday.

Greg Ulmer, the executive vice president of Lockheed’s Aeronautics unit, told reporters, “they’ve shown interest” in buying the jets, which are a big part of Lockheed’s revenue.

A representative from the Embassy of the Republic of Croatia in Washington said “we are evaluating an offer of the new U.S. F-16 Block 70/72 aircraft, together with some other responses to our tender for a multi-role fighter aircraft, new or used,” but did not address the F-35.

Croatia is evaluating U.S., French and Swedish offers for fighter jets as it looks to modernize its air force, which now flies Russian-made MiG-21 jets dating from its past within the former Yugoslavia.

Croatia wanted to buy 12 used F-16 fighter jets from Israel, but it fell through after Israel said here in 2019 it could not get approval from the United States for the sale.

Other international customers for the fifth-generation F-35 include Canada, Finland, and Switzerland, which are running competitions for a future jet purchase. Additional customer prospects for Lockheed’s F-35 include Greece, Spain, Eastern European and Middle Eastern countries, Ulmer said in a media conference call.

Lockheed has also seen international interest for as many as 300 of its fourth-generation F-16 fighter jets on top of the current production backlog of 128 jets, Ulmer said.