Croatia has urged Israel to overcome a rare 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 on Thursday it needed an answer from Israel by January 11 or the Balkan country's $500m 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 US approval for allowing the jets to go to a third party.

The deal ran into trouble after the US State Department hinted that Israel needs to strip off the upgrades that were added after Israel took delivery of the planes from the US 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 US.

"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.

Relations between the Trump administration and Israel have been very close, particularly on defence issues. But the sale of the jets to Croatia appears to be an exception.

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US Secretary of State Mike Pompeo and Israeli Prime Minister Benjamin Netanyahu met on Tuesday in Brazil but didn't agree on a way to end the impasse.

"We are expecting final and clear stands from both Israel and the United States on this issue and then we will make a final decision," Croatian Prime Minister Andrej Plenkovic said.

Croatian Defence Minister Damir Krsticevic said Thursday that Israel provided guarantees during the contract bidding process that US officials would greenlight the sale.

The controversy over the bid has triggered calls for the defence minister's resignation.

The deal is Croatia's largest single military buy since it split from the Yugoslav federation during the 1991-95 war.

NATO member Croatia faces a mini arms race with Russian ally Serbia, which recently received six used Russian MiG-29 fighter jets.