Delhi's chief minister accused India's leader on Tuesday of waging a political vendetta against him after federal investigators raided his administration's headquarters.
Doing away with political etiqette, Chief Minister Arvind Kejriwal accused Prime Minister Narendra Modi of ordering the police investigation and launched into a social media tirade - calling Modi a "coward and a psychopath".
Central Bureau of Investigation (CBI) officers raided the Delhi city government headquarters and 13 other locations in connection with a corruption case allegedly involving Kejriwal's principal secretary.
News of the police raid was broken by 47-year-old Kejriwal himself who posted on Twitter "CBI raids my office" before engaging in the personal attack on Modi.
The police bureau is independent, but critics have accused it of being under government influence.
Modi's ruling Bharatiya Janata Party (BJP) demanded an apology from Kejriwal - the leader of the anti-corruption Aam Aadmi Party - for his "unwarranted and shameful" description of the prime minister.
CBI called Kejriwal's comments "false propaganda".
Calls to BJP spokesman Nalin Kohli rang unanswered and were not returned.
Speaking to local TV station Times Now, Kohli said Kejriwal's outburst was "demeaning" to politics.
"He takes the oath as the chief minister of the union territory of Delhi, but does not even know the kind of language he has to use for an esteemed office - a constitutional post like the prime minister of India," Kohli said.
Kejriwal was unrepentant when he later addressed reporters.
"I have a message for Mr Modi: 'You can't scare me. You have no idea what I'm made of. I won't be afraid even until my last breath,'" he said.
It wasn't the first run-in between the bitter political rivals. Modi once called Kejriwal a "Pakistani agent" and an "anarchist who should join the Naxals [Maoist rebels] in the jungles".
Tuesday's police raid also triggered chaos in parliament. Finance Minister Arun Jaitley said it had "nothing to do" Kejriwal, and he ridiculed the suggestion it was politically motivated.
