The United States warns India against purchasing Russian weapons like advanced anti-aircraft systems or fighter jets, US Assistant Secretary of State Clarke Cooper told reporters on Thursday.

“The key point that has been shared with Indian counterparts… is: ‘Don’t put at risk future opportunities that may be impeded by significant Russian defence articles’”, Cooper said during an online briefing. “It’s not everything, but something like the [anti-aircraft systems] S-400 will be a challenge, something like the Sukhoi [fighter jet] Su-35 will be a challenge”.

Cooper said that Russian arms may not be interoperable with Western systems and pose threats of “potential exploitation of unique US technologies”.

The US is the second-largest defence exporter to India with sales reaching now $15 billion from near zero in 2008.