Tommy Tuberville is a member of the Senate Armed Services Committee

Washington: The US' relationship with India is deepening, a top Republican Senator has said, as he supported growing calls for a presidential CAATSA waiver to New Delhi on the purchase of S-400 missiles from Russia.

The S-400 is known as Russia's most advanced long-range surface-to-air missile defence system.

Senator Tommy Tuberville said he favours granting India a sanctions waiver for its purchase of the Russian S-400 missile-defence system.

"Our relationship with India is deepening. We met with Prime Minister (Narendra) Modi and high-ranking officials to discuss Chinese aggressions toward India," Senator Tommy Tuberville said on Tuesday.

The Senator was part of a Congressional delegation to India and Southeast Asia to have a first hand impression of the dangers being posed by China in the region.

Talking about CAATSA, he said, "I think it should be waived," Politico reported on Monday.

"We would have loved (for them) to have an Aegis system or a Patriot system ... but they decided to go another direction. So we'll see what Congress and President Biden say about this," he was quoted as saying.

The US has expressed its "concern" over the delivery of S-400 Triumf surface-to-air missile systems from Russia to India.

The Biden administration has not yet clarified whether it will impose sanctions on India under the provisions of the Countering America's Adversaries Through Sanctions Act (CAATSA) for procuring the S-400 missile systems.

The CAATSA, which was brought in 2017, provides for punitive actions against any country engaged in transactions with Russian defence and intelligence sectors.

In October 2018, India had signed a USD 5 billion deal with Russia to buy five units of the S-400 air defence missile systems, despite a warning from the then Trump administration that going ahead with the contract may invite US sanctions.

The US has already imposed sanctions on Turkey under the CAATSA for the purchase of a batch of S-400 missile defence systems from Russia.

Following the US sanctions on Turkey over the procurement of S-400 missile systems, there were apprehensions that Washington may impose similar punitive measures on India.

Russia has been one of India's key major suppliers of arms and ammunition.

There are growing calls in the US urging the Biden administration to grant CAATSA waiver to India.

In October, two powerful US Senators -- Mark Warner of the Democratic Party and John Cornyn of the Republican Party -- had urged President Biden not to impose provisions of CAATSA against India for buying the S-400 missile system as it is in America's national security interest.

"We strongly encourage you to grant a CAATSA waiver to India for its planned purchase of the S-400 Triumf surface-to-air missile system. In cases where granting a waiver would advance the national security interests of the US, this waiver authority, as written into the law by Congress, allows the President additional discretion in applying sanctions," they wrote in a letter to Biden.

Both Warner, Chairman of the Senate Permanent Select Committee on Intelligence, and Cornyn, Senate Minority Whip for the Grand Old Party (GOP), are co-chairs of the powerful Senate India caucus, the only country specific caucus in the US Senate.

Talking about his visit to India, Tuberville said, "I was heartened that" Prime Minister Modi "not only committed to continue support of our Freedom of Navigation Operations, but that India will increase them," he said.

Tuberville is a member of the Senate Armed Services Committee.