U.S soldiers walk next to a Patriot missile defence battery during join exercises at the military grouds in Sochaczew, near Warsaw, March 21, 2015. REUTERS/Franciszek Mazur/Agencja Gazeta

WASHINGTON (Reuters) - The U.S. State Department has approved the possible sale of Patriot missile defense systems worth $3.9 billion to Romania, a Pentagon agency said in a statement on Tuesday.

The prime contractors would be Raytheon Co RTN.N and Lockheed Martin Corp LMT.N, the Defense Security Cooperation Agency said.