Tharoor has been in the eye of a storm since Sunday when news broke that a female friend - said to be his girlfriend - had been granted a free stake in a new franchise of the glitzy Indian Premier League (IPL).

Tharoor had helped to put together the consortium that bought the Kochi team - in Kerala, the state he represents in Parliament - and the opposition has alleged that the free stake worth $15 million was a “consideration” for his services. The main opposition Bharatiya Janata Party has demanded he resign and the Communist Party of India (CPI) echoed the call on Wednesday, urging the 54-year-old to step down until his name is cleared.

“The whole episode is getting murkier and murkier. Tharoor’s continuation in the job has become untenable. He should quit,” D. Raja, senior leader of the CPI told AFP.

The Congress party, which Tharoor joined in 2008, initially backed him, but has since fallen silent. Prime Minister Manmohan Singh said during a visit to Washington that he is seeking details on the controversy.

Tharoor, who spent almost three decades in the United Nations before quitting in 2007, was elected MP from Thiruvananthapuram, capital of southern Kerala state last year. He has denied allegations of impropriety, saying he had “neither invested nor received a rupee for my mentorship of the team.

“Whatever my personal relationships with any of the consortium members, I do not intend to benefit in any way financially from my association with the team now or at a later stage,” he said in a statement posted on his website. Tharoor made many enemies in the Congress when the “rank outsider” was elevated to the post of junior minister Singh.

The free stake was revealed by the IPL chief Lalit Modi, who leaked the details on microblogging website Twitter.

The former UN communications chief has since infuriated many Congress leaders with his “tweets” on Twitter on government austerity measures and public remarks seen as critical of government policy.

Meanwhile, a police team on Wednesday visited Tharoor’s residence here to investigate an SMS threat he has received, police sources said. Officials from the Tughlak Road police station went to the minister’s Lodhi Estate residence and spent about an hour.

“We (came) to inquire SMS threats to the minister after seeing reports in the media. We were not called by the minister,” a team member told reporters. Officials said no case had been registered.

A Delhi Police spokesman, however, denied knowledge of any such development. Jacob Joseph, the officer on special duty with the minister, told reporters that Tharoor had received the SMS threat and the Home Ministry and police had been alerted.