Delhi Chief Minister Arvind Kejriwal on Thursday took on Prime Minister Narendra Modi after former aide Rajendra Kumar, seeking retirement from government service, alleged that the CBI was pressurising him to implicate the Aam Aadmi Party leader.

"CBI raids my office, pressurises officer to implicate me. CBI raids Satinder Jain's office. Why are you so so scared of us Modiji? Chill!" Kejriwal tweeted, referring to CBI's December raid on Delhi Health Minister Satyendar Jain's OSD Nikunj Aggarwal's office and Kumar's allegations.

IAS officer Rajendra Kumar, Kejriwal's former Principal Secretary, earlier said he has tendered voluntary retirement request claiming officials at the Central Bureau of Investigation were pressurising him to name the "Chief Minister".

Rajendra Kumar claimed that the Central Bureau of Investigation officials were pressurizing him to implicate the "Chief Minister" in the alleged wrongdoings he (Kumar) is accused of.

"I tender my voluntary retirement (VRS) request to the government from the services," Kumar told reporters here.

"It was a very difficult decision and I have taken this decision with a very heavy heart... as the government has provided me a medium to work for the people.

"There are many other ways to work for public welfare and I will seek those," he said.

"The government has given me a lot," he said.

"Despite coming from a very poor family, the government gave me an opportunity to study in a very prestigious school and then also allowed me to serve for the government for 27 years, I am obliged for that."

Kumar was arrested on July 4, 2016 in a corruption case. In December 2016, the CBI filed a chargesheet against Kumar.

Kumar, a 1989-batch IAS officer, was accused of abusing his official position in awarding Delhi government contracts worth Rs 9.5 crore to private firm, Endeavour Systems Pvt Ltd.

Kumar was granted bail on July 26. He has denied the accusations hurled against him.

"I will stay in the public service forever till my last breath that is my determination," Kumar said. "And no hurdle can distract me."

Asked if the CBI pressurised him to name Kejriwal in the case, Kumar said: "Whatever I have said is the exact truth and I stand by it.

"I have already written in my VRS the main aim of the government (whichever it may be) was to put pressure on me to incriminate certain people, including Chief Minister Kejriwal," he added.