A Russian-designed Indian nuclear submarine, considered a key platform in the country's second strike capability, has suffered major damage and has been undergoing repair for over 10 months, The Hindu newspaper said on Monday.

It said the damage to INS Arihant may have been caused by a possible human error and the vessel had not sailed now for months.

Arihant's propulsion compartment suffered damage after water entered the area more than 10 months ago, according to details available with the paper.

One naval source said water rushed in because a hatch on the rear side was left open by mistake.

The ministry of defence did not respond to questions from The Hindu.

The indigenous nuclear submarine, built under the Advanced Technologyinfo-icon Vessel project, suffered damage while it was at harbour. Since the accident, the submarine has been undergoing repair and clean-up, and has not sailed, sources said.

Besides other repair work, many pipes had to be cut open and replaced. One naval source said the 'cleaning up' is a laborious task in a nuclear submarine which is why there has been a delay in getting it back to sea.

Arihant's issue has arisen soon after INS Chakra, the nuclear submarine leased from Russiainfo-icon, was reported to have suffered damage to its sonar domes while entering the harbour in Visakhapatnam in early October, the paper said.

"However, INS Chakra has only a peripheral role in the nuclear triad, for both training and escorting, since it is INS Arihant that would carry nuclear missiles," the paper said.

The absence of Arihant from operations came to the political leadership's attention during the Indiainfo-icon-Chinainfo-icon military standoff at Doklam. Whenever such a standoff takes place, countries carry out precautionary advance deployment of submarine assets, according to the report.