The US has activated a land-based missile defence station in Romania, which will form part of a larger and controversial European shield.
Senior US and Nato officials are attending the ceremony in Deveselu, southern Romania.
The US says the Aegis system is a shield to protect Nato from short and medium-range missiles, particularly from the Middle East. But Russia sees it as a security threat – a claim denied by Nato. Relations between the West and Russia have deteriorated since Moscow’s annexation of Ukraine’s southern Crimea peninsula in 2014. Russia is also accused of arming separatists in eastern Ukraine and sending its troops there – a claim denied by the Kremlin.
Nato Secretary General Jens Stoltenberg and other senior officials from the military alliance are at the opening ceremony at an old Romanian air base in Deveselu. The US is believed to have spent $800m (£554m) on radar and SM-2 missile interceptors since 2013. The station will have a battery of SM-2 missile interceptors.
Nato and US officials say the system has been developed to track and intercept missiles fired from a “rogue” state. In the past Iran was mentioned in that context, but the US has also had North Korea in mind.
For years the US has been testing the Aegis system on warships too. The officials also stress the shield is not directed against Russia. “Both the US and Nato have made it clear the system is not designed for or capable of undermining Russia’s strategic deterrence capability,” US Assistant Secretary of State Frank Rose said on Wednesday. “Russia has repeatedly raised concerns that the US and Nato defence are directed against Russia and represents a threat to its strategic nuclear deterrent. Nothing could be further from the truth,” he added.
Russia’s foreign ministry warned on Wednesday that the system violated a treaty on nuclear forces.
A ministry statement quoted by Interfax news agency said it was a breach of the Intermediate-Range Nuclear Forces (INF) Treaty, signed in 1987. “This decision is harmful and mistaken, because it is capable of upsetting strategic stability,” said Mikhail Ulyanov, head of the Russian foreign ministry’s department for proliferation and arms control issues.
An incoming missile would be destroyed in space, before it could re-enter the Earth’s atmosphere.
On Friday, another phase of the project will be launched in Poland with a groundbreaking ceremony at Redzikowo, near the Baltic Sea. Aegis missiles are to become operational there in 2018.
Mr Ulyanov said Russia’s interests “are being affected in a direct way by this”. He said the Americans’ MK-41 launch system could also be used to fire cruise missiles, not just air defence missiles. “From our viewpoint this is a violation of the Intermediate-Range Nuclear Forces Treaty,” he said.