India police on Wednesday detained opposition leaders as they tried to meet the family of an ex-serviceman who allegedly killed himself over the government's pension policy for army veterans.

Top politicians, including Congress Vice President Rahul Gandhi and Delhi state's Chief Minister Arvind Kejriwal, were detained from a hospital in separate police stations.

The veteran, named by Indian media as Ram Kishan Grewal, died on Tuesday.

The pension scheme, approved by Indian Prime Minister Narendra Modi's government last September, was expected to benefit around three million veterans by giving them more money every five years regardless of when they retired.

But some veterans are angry the government has not met all their demands, including the pension increase.

“I only wanted to speak with them [family of the veteran) for two minutes but they detained me and even the family of the veteran. What did they do?” said Rahul Gandhi.

“This government should at least apologise to the veteran's family,” he said.

“During protest by political parties at the hospital today, none has been arrested,” said Delhi police on social media, adding the politicians were detained after “medical services (at the hospital) got severely affected and orderliness deteriorated”.

Gandhi later urged Indian prime minister on Twitter to implement the One Rank One Pay (OROP) pension scheme in a meaningful way.

Kejriwal hit out at Modi on Twitter during his detention.

“PM Modi is lying that OROP has been implemented. If it was implemented, why would likes of Ram Kishan commit suicide? Mr Modi should apologise to the soldiers,” he tweeted in Hindi.

OROP was one of the longest pending demands made by Indian army veterans from successive New Delhi governments. Modi made it one of his key poll promises during his election campaign.