The Delhi Police confirmed on Friday that Sunanda Pushkar, the late wife of former union minister Shashi Tharoor, had been poisoned and her death was "unnatural".

The Federal Bureau of Investigation (FBI) report, which has been sent to AIIMS for further examination, confirms the Delhi Police's claim. However, the FBI ruled out the use of radioactive poisoning. An initial AIIMS report had claimed that she overdosed on anti-depressant pills, but the Delhi Police remained firm on their "poisoning" claim. The conflicting reports led to her samples being sent to the FBI for analysis.

"As far as evidences are concerned until now, Sunanda Pushkar's death was unnatural," Delhi Police Commissioner BS Bassi told ANI. "All conclusions shall be examined, and then decide future course of action," he added.

According to sources, the FBI mentioned the presence of a dangerous chemical that was administered through an injection, said ANI. The FBI analysis established that the death occurred due to the same poison, which was present in the viscera.

"We are studying the report, once we analyse the content we will continue with our investigation," Delhi Police Commissioner BS Bassi said about the AIIMS report.

Before her untimely death on 17 January, 2014, Pushkar, 53, was married to Shashi Tharoor for almost four years. Her death came on the heels of her publicly accusing Tharoor of having an extra-marital affair with Pakistani journalist Mehr Tarar. The Delhi Police launched an investigation soon after her body was found in a luxury hotel in Delhi.

The death was booked as a murder and six people have taken the polygraph test during the course of investigation. However, the police have not registered a main accused yet.

Tharoor has also been questioned multiple times about the murder as he was present in the hotel that night. He has maintained that he is cooperating with the police, reported NDTV.