The United States has said it approved a 3.5-billion- U.S.-dollar sale of Patriot air and missile defense systems to Turkey amid tensions between the NATO allies over Ankara's plans to buy similar systems from Russia. 

The State Department said on Wednesday it had notified Congress of plans to sell Turkey a Patriot package that includes 80 Patriot guidance-enhanced missiles and 60 PAC-3 missile interceptors and related equipment. 

It's reported that the proposed sale will increase the defensive capabilities of the Turkey military to guard against hostile aggression and shield NATO allies who might train and operate within Turkey's borders.

The State Department said earlier this year it was working with NATO ally Turkey on the possible sale of a Raytheon Co Patriot missile defense system to keep it from buying a Russian-made S-400 system, which Ankara announced a year ago. 

U.S. and NATO officials have repeatedly warned Ankara that the Russian system cannot be integrated into the NATO air and missile defense system and that purchasing the S-400 system would jeopardize Turkey's purchase of Lockheed Martin Corp F-35 fighter jets and possibly result in Washington imposing sanctions.

"It is important that NATO countries procure military equipment that is interoperable with NATO systems. A Russian system would not meet that standard," an official said on condition of anonymity. 

The notification process alerts Congress that a sale to a foreign country has been approved, but it does not indicate that a contract has been signed or negotiations have concluded.

The announcement came hours after U.S. President Donald Trump said the U.S. had defeated the ISIL group in Syria, leading to the withdrawal of U.S. troops, who are located in the Kurdish-controlled north of the country.

There was no immediate indication that the two announcements were linked, though Trump has all along made it clear that arms sales are a top priority for him.

(With inputs from agencies)