The proposed sale has run into a road block with the United States reportedly insisting that Israeli equipment be removed from the planes before the sale could proceed.

Croatia urged Israel to overcome disagreement with the United States and to confirm it can carry through on a deal to sell 12 used American-made fighter jets.

Croatia’s Defence Ministry said it needed an answer from Israel by Jan. 11 $500 million order for a dozen F-16 aircraft would be cancelled.

Israel made a tentative deal to sell the upgraded F-16 Barak fighters to Croatia in March pending U.S. approval for allowing the jets to go to a third party.

The deal ran into trouble after the U.S. State Department hinted that Israel needs to strip off the upgrades that were added after Israel took delivery of the planes from the U.S. some 30 years ago.

Israel upgraded the jets with sophisticated electronic and radar systems, which was crucial in Croatia’s decision to buy the planes from Israel rather than from the U.S.

“If the planes are not in accordance with what we have agreed, the deal will not be carried out and we will have another purchase bid,” Croatia’s parliament speaker, Gordan Jandrokovic, said.