President Donald Trump had a very good personal relationship with Prime Minister Narendra Modi, but “that's gone now”, US' former National Security Adviser John Bolton has said, cautioning that close ties with the American leader "won't protect" world leaders from the "worst".

Bolton's remarks came against the backdrop of possibly the worst phase in India-US relations in over two decades, with the strain exacerbated by Trump's tariff policy and constant criticism of New Delhi by his administration.

“I think Trump sees international relations through the prism of his personal relations with leaders. So if he has a good relationship with Vladimir Putin, the US has a good relationship with Russia. That's obviously not the case,” he said in a recent interview with British media portal LBC.

Bolton, who served as NSA in the first Trump administration, has been very critical of his former boss.

“Trump had a very good relationship personally with Modi. I think that's gone now, and it's a lesson to everybody, for example, (UK Prime Minister) Keir Starmer, that a good personal relationship may help at times, but it won't protect you from the worst,” he said.

Trump is scheduled to visit the UK from September 17 to 19.

In a post on social media accompanying his interview with LBC, Bolton said the White House has "set US-India relations back decades, pushing Modi closer to Russia and China. Beijing has cast itself as an alternative to the US and Donald Trump”.

The former NSA said Trump's treatment of India over the past several months has undermined years of bipartisan US efforts to wean New Delhi away from its Cold War alignment with Russia and to ensure Indian policymakers across the spectrum recognise China as their principal security challenge.

“That has been reversed. I think it can be reversed again, but it's a very bad moment," he said.

Bolton has earlier said that the tariffs imposed by the Trump administration on India for its purchase of Russian oil may have pushed New Delhi closer to the Beijing-Moscow axis, describing it as an “unforced error”.

Bolton's Maryland home and Washington office were recently searched by the FBI as part of a criminal probe into the alleged mishandling of classified material.

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