New Delhi, Jan 27 (IANS): A women's group Monday demanded a thorough investigation into the mysterious death of Sunanda Pushkar, wife of union minister Shashi Tharoor.

The All India Democratic Women's Association (AIDWA) expressed concern at the "arbitrary and non-serious way" in which the probe into the death of Pushkar is being carried out.

"The case has been transferred back to the south district (police) from the Crime Branch without providing justified reasons," the AIDWA said in a statement.

The association demanded the reasons behind the transfer to be "spelt out clearly".

In the statement, the AIDWA said the transfer only "raised suspicions" about chances of "external interventions" in the case which involves Tharoor.

Pushkar was found dead under mysterious circumstances in her room at a hotel in south Delhi Jan 17.

"It has been 10 days since her death, and so far there hasn't been any police investigation. Moreover, there are reliable reports suggesting that some instructions were being given to close the case files by putting it in 'cold cases cell'," it said.

AIDWA added that Pushkar's autopsy reports specified injury marks on her body and that the investigation agencies were "duty bound to establish whether violence or foul play was involved" in her death.

It also suggested that investigation agencies ascertain Tharoor's role in the matter.

"AIDWA feels that there should be a fair, thorough and speedy investigation into this case. No 'clean chits' should be given to people involved, either by police or ministers before the investigation is over," the statement said.