NEW DELHI: Indian Prime Minister Narendra Modi says he will seek to unravel one of India's most enduring mysteries surrounding the independence struggle, the latest salvo in a growing history war that could undermine the opposition Congress party.

The fate of Subhas Chandra Bose, leader of the Indian National Army which collaborated with the Japanese and Germans against the British in World War Two, has remained a riddle for seven decades.

Successive Indian governments have kept hundreds of files related to his death secret, saying the release of the information could prejudice relations with foreign nations, fuelling conspiracy theories about how he died.

Modi's decision this week to declassify all files on India's most enigmatic nationalist hero may finally end the controversy.

The findings could also embarrass India's most famous political dynasty, because of the role played by first Prime Minister Jawaharlal Nehru in the aftermath of Bose's death.

Since trouncing the Nehru-Gandhi family's Congress party in a general election last year, Modi has chipped away at its grip on India's post-colonial history.

Modi's government has announced plans to change a museum set up to honour Nehru so it will reflect a wider range of leaders. His government has also erased the names of Nehru and his descendants from government schemes, places and postage stamps.

At a meeting on Wednesday, Modi met Bose's relatives to tell them the files would be declassified from January onwards to coincide with his 119th birthday.

"By ending the speculation it will allow us to assess his full contribution to the independence movement," said Sidharth Nath Singh, a leader from Modi's Bharatiya Janata Party (BJP), who met the Bose family.

The Indian government has officially said Bose died of burns when his aircraft crashed in Taiwan while he was on his way to Tokyo, three days after the end of World War Two.

Many Indians refuse to believe that. Some think he faked his own death to avoid capture, with reports saying he lived in the Soviet Union or in India disguised as a holy man.

A six-year inquiry headed by a Supreme Court judge found in 2006 that neither Taiwan nor the United States had any record of his plane crashing. It also found his supposed ashes in a shrine in Tokyo were those of a soldier.

Political ramifications

Singh said the release of the files could embarrass Congress if they showed that Nehru's government thought he was alive but did not want him to return to public life.

"The release of the files does have political ramifications, you can't ignore it," said Singh.

Nehru's government spied on Bose's family for two decades, suggesting it thought he may be alive, files declassified by West Bengal's government last month show.

Campaigners believe files held by the central government will provide greater clarity on his fate.

Congress veteran Mani Shankar Aiyar said the files will exonerate Nehru, and the reason they were kept secret is that they probably embarrass a foreign ally, but enough time has passed for it not to matter. "The idea that they will embarrass Nehru is pure BJP fantasy," said Aiyar.

About 200-300 files held by the prime minister's office, intelligence bureau and foreign ministry will be declassified, Singh said.

Bose campaigned against British colonial rule with Mahatma Gandhi for 20 years, but fell out with him because he believed non-violence would fail.

To millions of Indians, he was a patriot who took a heroic stance against British imperialism and who has failed to get sufficient recognition in independent India.

Bose escaped from house arrest in India in 1941 to travel to Germany, where he met Adolf Hitler and later boarded a German submarine bound for Japan.

Bose eventually arrived in Myanmar as the head of the Indian National Army, which fielded Indian troops drawn from prisoners of war taken by the Japanese.

The last known photograph of Bose shows him stepping off a plane in Vietnam, a day before his purported death.

No photograph of his body or death certificate has been published.

Chandra Kumar Bose, a relative of the leader, welcomed Modi's decision to release the files.

"We do not know for sure what happened to him, but of the many theories the plane crash theory should be debunked," he said.