FILE- In this Tuesday, June 7, 2011 file photo, a US Navy officer, name not available, stands on the weapons control deck of the USS Monterey as screens display the Black Sea region, in the Black Sea port of Constanta, Romania. A U.S. missile defense system aimed at protecting Europe from ballistic missile threats is moving into higher gear this week, with a site in the village of Deveselu, Romania becoming operational on Thursday, May 12, 2016, and officials breaking ground at a separate site in Poland a day later.(AP Photo/Vadim Ghirda, File)

DEVESELU, Romania - A U.S missile defence site in Romania aimed at protecting Europe from ballistic missile threats became operational Thursday, drawing an angry reaction from Russia, which opposes having the advanced military system in its former area of influence.

NATO Secretary-General Jens Stoltenberg tried to reassure Russia as he spoke at a ceremony attended by U.S., NATO and Romanian officials at the Soviet-built base, located in remote village 180 kilometres (110 miles) southwest of Bucharest. Romania became a NATO member in 2004.

The NATO missile defence site "in no way undermines or weakens Russia's strategic nuclear deterrent. This site in Romania, as well as the one in Poland, are not directed against Russia," Stoltenberg said at the opening ceremony. "The interceptors are too few, and located too far south or too close to Russia, to be able to intercept Russian intercontinental ballistic missiles."

Stoltenberg said the interceptors were designed "instead to tackle the potential threat posed by short and medium- range attacks from outside the Euro-Atlantic area."

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.

Stoltenberg noted that Moscow had unilaterally terminated co-operative dialogue about missile defence in 2013.

Earlier, he said Russia had "changed borders by force and continues to intimidate its neighbours," in reference to the annexation of Crimea from Ukraine in 2014.

He said, however, the alliance would continue to try and engage Russia in dialogue where possible.

"In times of tension, keeping channels of communication open is even more important," he said.

Russian President Vladimir Putin's spokesman, Dmitry Peskov, said Moscow was already taking measures for "securing the necessary level of security in Russia," and Foreign Ministry spokeswoman Maria Zakharova raised the tone saying: "We continue to regard the destructive activities of the USA and its allies in the area of missile defence as a direct threat to international and regional security."

Adm. Vladimir Komoyedov, chairman of the State Duma's defence committee, called the missile defence site a threat to Russia.

"This is a direct threat to us," Komoyedov, the former commander of the Russian Black Sea Fleet, told the Interfax news agency. "They are moving to the firing line. This is not just 100 — it's 200, 300, 1,000 per cent aimed against us."

"This is not about Iran, but about Russia with its nuclear capabilities," he said.

President Klaus Iohannis said Romania wanted NATO to have a "permanent naval presence" in the Black Sea that respected international conventions, and called for increased security for alliance members in the south and east, which border Russia and the Middle East.

"It is important that a credible and predictable presence can be assured of the allied forces on the eastern flank, to balance the northern dimension with the southern and eastern flank," Iohannis said after meeting Stoltenberg on Thursday in the Romanian capital, Bucharest.

On Friday, Polish and U.S. officials will take shovels in hand to break ground at a planned missile defence site in the Polish village of Redzikowo, near the Baltic Sea.

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Nataliya Vasilyeva and Lynn Berry in Moscow contributed to this report

News from © The Associated Press, 2016