ZAGREB (Reuters) - Israel will not be able to deliver to Croatia a dozen used F-16 fighter jets which Croatia decided to buy last year to modernize its air force, Croatia’s Defense Minister Damir Krsticevic said on Thursday.

“Israel has officially informed us that it cannot get an approval from the United States for delivery of the planes to Croatia,” Krsticevic told reporters after a meeting with an Israeli delegation in Zagreb.

Officials from both sides said Croatia held no responsibility for the deal falling through. They gave no comment on why the United States opposed the sale.

Croatian media reported the problem arose as the planes have been refitted with Israeli technology, depriving U.S. defense companies the chance to update and service the planes.

The U.S. State Department did not comment because it was on furlough.

Croatia’s Prime Minister Andrej Plenkovic said earlier this week that Zagreb would not accept any other deal but the original Israeli offer which it accepted last March.

“The agreement on buying the planes has not been signed, so there is no financial damage to our budget,” Plenkovic told a cabinet session on Thursday.

He added that Croatia was determined to continue with its plans of modernizing its air force. It is unclear at the moment whether Zagreb would now call another tender or turn to other bidders that competed in a previous tender.

The deal with Israel was supposed to be worth $500 million.

Israel had been in competition with several countries bidding for Zagreb’s business. Sweden’s SAAB was reported as being the most serious competitor, offering new Gripen planes, but at a much higher price.

Croatia joined the NATO alliance in 2009 and the EuropeanUnion in 2013. Its air force currently owns a squadron of outdated MIG-21 fighter jets, but just three planes are operational at the moment.