LONDON — Thirty years after Indian troops stormed the Golden Temple at Amritsar, leaving hundreds dead, the British government said Tuesday that it would open an investigation after the release of documents suggesting that British special forces had helped to draw up a plan to attack the building.

The June 1984 raid on the temple, the holiest shrine for Sikhs, was intended to flush out separatists and, according to the Indian government, killed about 400 people. Sikh groups estimate that many more were killed, and the raid caused outrage among Sikhs around the world.

The internal government documents were published on a British blog, Stop Deportations, which said that they had been released under rules allowing for the publication of government records after 30 years, but that they had been “buried” beneath other documents made public on Jan. 1.

One letter, dated Feb. 6, 1984, from the office of Britain’s prime minister at the time, Margaret Thatcher, mentioned the “Indian request for advice on plans for the removal of dissident Sikhs from the Golden Temple,” adding that Mrs. Thatcher was “content that the foreign secretary should proceed as he proposes.”