Indian police said Wednesday that they are now treating the death of the wife of a prominent former government minister and U.N. diplomat as a murder and have set up a special team to investigate her death in a New Delhi hotel last year.

Sunanda Pushkar's death last January was previously believed to have been a suicide. But Delhi police chief Bhimsen Bassi said Wednesday that after an investigation, a medical board had concluded that she had been poisoned.

A murder case has been registered and a team of police officials will re-examine all those linked to the case, Bassi said.

Pushkar's husband was Shashi Tharoor, a former junior minister and U.N. undersecretary-general.

It is not clear what type of poison was used to kill Pushkar. Bassi said medical samples would be sent to laboratories abroad to determine the nature and quantity of the poison.

Tharoor said he wanted a comprehensive investigation so the truth about his wife's death would become known. "I am anxious to see this case is investigated thoroughly and continue to assure the police of my full cooperation," he said.

Tharoor was U.N. undersecretary-general for communications and public information under former Secretary-General Kofi Annan. His name was among those considered for the top U.N. post in 2006, when Ban Ki-moon was voted in.

In 2009, Tharoor won a seat in India's Parliament from the southern state of Kerala and later became a minister in then-Prime Minister Manmohan Singh's government.

The couple married in 2010 and frequently figured in the society pages of newspapers and on social media.