The US State Department said Tuesday it is ready to approve the sale of Patriot air defense systems to Romania, a $3.9 billion deal likely to infuriate Russia.

"The State Department has made a determination approving a possible foreign military sale to Romania for Patriot air defense systems, related support and equipment," the State Department said.

Congress has 30 days to raise objections to the sale, though this is unlikely given that Romania is a NATO partner.