Iraq has signed an agreement to buy 18 fighter jets from U.S. defense company Lockheed Martin, in a move to bolster its air defenses.

An advisor to Prime Minister Nouri al-Maliki said Tuesday Iraq has made an initial payment for the F-16 warplanes, but did not specify the cost of the deal.

The agreement comes after Iraq saw a surge in oil revenue this year, and the country has said it is looking to buy 36 jets in total.

The government abandoned a potential $900 million deal for fighter jets earlier this year, instead routing the money to welfare programs.

Lockheed Martin said in a statement it welcomes Iraq as the 26th nation to operate the F-16.

The remaining U.S. forces in Iraq are due to withdraw by the end of the year. U.S. and Iraqi officials have said Iraqi forces are capable of maintaining internal security, but need training in using heavy weaponry to defend the country’s borders, airspace and territorial waters.