India's Prime Minister Narendra Modi with President of America Donald Trump (image: hwnews)

India's purchase of the Russian S-400 Triumf missile defense systems will have "serious implications" on the Indo-US defense ties, a top US state Department official said Friday.

"The Trump administration has been very clear that the acquisition of advanced Russian technology sends the wrong message to Russia at a time when it continues its aggressions," the official added.

"As we (US and India) have discussions about combat aircraft sales and other advanced systems, the decisions that India makes with regard to S-400 will have an impact on those conversations."

Acquiring S-400s from Russia, according to the official, will have an impact on the military relations, irrespective of whether the country increases its military purchase from the US or not.

"The S-400 is significant because of CAATSA sanctions. It is also significant because of what it precludes, in terms of future high-tech cooperation," the official said.

The US also threatened imposing Countering America's Adversaries Through Sanctions Act (CAATSA) against Turkey if it goes ahead with the Russian S-400 Air Defence Systems deal, the State Department warned on Wednesday.

This is the first instance of the US intending to invoke CAATSA against a country for buying Russian equipment since the act came into force in 2018.

"Turkey will face very real and very negative consequences if it completes the delivery of the S-400," State Department spokesperson Morgan Ortagus had said.

"You can look at the very serious conversation that is taking place with our NATO partner Turkey and the same concerns will apply should India proceed with an S-400 purchase," the top source from the US state department said.

Washington has already offered the US-made Lockheed Martin Terminal High Altitude Area Defense (THAAD) and Raytheon’s Patriot Advance Capability (PAC-3) missile defense systems for New Delhi and Ankara as an alternative to the Russian systems.

India and Russia signed a $5 billion contract for S-400 systems in October 2018. The deliveries are expected to commence from October 2020 and conclude by April 2023.