A U.S missile defense site in Romania aimed at protecting Europe from ballistic missile threats becomes operational, angering Russia which opposes having the advanced military system in its former area of influence.

NATO Secretary General Jens Stoltenberg is due to speak at a Thursday ceremony attended by U.S., NATO and Romanian officials to mark the start of operations at a base built by the Soviet Union, some 180 kilometers (110 miles) southwest of Bucharest.

A day later Polish and U.S. officials will take shovels in hand to break ground at a planned site in the Polish village of Redzikowo, near the Baltic Sea.

U.S. officials say the Romanian missile shield which cost $800 million is intended to fend off missile threats from Iran and is not aimed at Russia.