India's federal police have conducted raids on offices and residences linked to founders of NDTV, the country's oldest English-language news channel, which termed it a "witch-hunt" and an attempt to "undermine free speech".

"NDTV and its promoters will fight tirelessly against this witch-hunt by multiple agencies. We will not succumb to these attempts to blatantly undermine democracy and free speech in India," the broadcaster, which is seen as critical towards the government of Prime Minister Narendra Modi, said in a statement on Monday.

It dismissed the raids as "concerted harassment of NDTV and its promoters based on same old, endless false accusations".