The United States is blocking an arms deal that would see 12 US-made F-16 warplanes being sold by Israel to Croatia, political sources in Tel Aviv said. According to the sources, the $500 million deal, reached by Israeli Prime Minister Benjamin Netanyahu and his Croatian counterpart Andrej Plenkovic in January, has infuriated Washington. The deal was officially announced in March. Officials close to US President Donald Trump and the State Department have backed it despite criticism by the Pentagon, the Treasury and intelligence agencies. Eventually, the administration agreed to announce its disapproval of the deal, sending letters to the Israeli government to prevent the sale. Israel has reportedly angered the Trump administration by adding advanced Israeli-made electronic systems to the F-16s as part of efforts to convince Croatia to buy the planes. The sources said Washington believes Israel unfairly profited through its actions, as the F-16s are American-made and were not supposed to be sold to a third-party without its approval. But the delay in the deal’s implementation has angered top Croatian officials, who have lately sent letters to Israel asking it to swiftly resolve its problems with the US administration. According to the sources, Netanyahu discussed the issue with US Secretary of State Mike Pompeo in Brussels on Monday. Pompeo reportedly said it was not him blocking the deal, laying blame on US Secretary of Defense James Mattis. Israel has been seeking a buyer for the aging fleet that its air force stopped using a number of years ago. It reportedly wants to replace the F-16s with advanced F-15 warplanes.