A controversial order of Israeli-made Heron unmanned aerial vehicles passed critical performance tests in Israel and will soon be delivered, Turkey's top procurement official says.

"Six of the aircraft have successfully passed the tests inspected by a delegation of Turkish officials," Murad Bayar, head of the government's defense procurement agency, the Under Secretariat for Defense Industries was quoted telling local media. "We are expecting their deliveries in the weeks ahead. And this closes the deal from our point of view."

Similar performance tests will take place in the next few months for the remaining four UAVs included in the program.

Turkey awarded the lucrative contract five years ago, placing the order with Israel Aerospace Industries and Elbit. Both companies beat out major U.S. competitors but the contract was bogged from a start with delays stemming from technical problems.

The contract deadline was initially set at 24-30 months. But both contracts missed the first deadline, breaching, also, a follow-up delivery date for the dispatch of four Herons last August.

With the deal dogged by problems, the Turkish government threatened to pull the plug on the order, saying it would seek financial damages from the Israeli contractors.

Last December, however, Ankara announced its intention to speed up the deal.

The order is estimated at $183 million, of which $50 million is set to go to Turkish Aerospace Industries and Aselsan. While the bulk of the project rests with IAI and Elbit, TAI is the Heron program's prime contractor.

The Turkish daily Hurriyet reported that under the revised deal the manufacturing team will pay compensation of nearly $18 million to Turkey for the delays and failure to meet some of the criteria in the program's original specifications.

"The compensation will be divided among the drones' manufacturers, including the Turkish companies taking part in the program, in line with their shares in the contract," the newspaper reported.

It is expected to be paid out in equipment and services, rather than in cash.

Major militaries round the globe have been increasing their use of UAVs for reconnaissance, surveillance and, at times, offensive purposes.

Muslim but secular Turkey has had a strong history of military cooperation with Israel. It has also acted as an intermediary for the Jewish state with the Arab world. Yet the Heron dispute aggravated relations late last year, forcing senior Israeli officials to meet with high-level government officials to try and mend ties.

It is understood that some of the drones to be delivered to Turkey will be deployed along the country's southeastern province of Batman, on the border with Iraq, for additional tests.