The S-400 air defense systems are a new generation of long anti-aircraft missile systems.

India's Foreign Minister announced Monday that Russia has begun delivering to his country the Russian S-400 ground-to-air missile defense system, against which the US threatened to impose sanctions.

"Supplies have begun this month and will continue to happen," Indian Foreign secretary Harsh Vardhan Shringla confirmed after Russian President Vladimir Putin's visit to New Delhi.

Praising India at the beginning of his visit to New Delhi, Putin is expected to discuss defense agreements, military relations, and energy cooperation between the two countries.

"We perceive India as a great power, a friendly nation and a time-tested friend," Putin expressed in the Indian capital alongside India's Prime Minister Narendra Modi.

Earlier, the United States warned of imposing sanctions under the Countering America's Adversaries Through Sanctions Act (CAATSA), in an attempt to smother Russia. The State Department said last week that no decisions had been made on any waivers for India.

It is noteworthy that Russia and India signed a contract to supply the S-400 systems in October 2018, in a deal estimated at $5.43 billion, thus making India the third foreign buyer of this system after China and Turkey.

The S-400 air defense systems are a new generation of long anti-aircraft missile systems.