India is building a nuclear submarine, a top Indian scientist has reportedly said, confirming long-running rumors of the secret naval project.

The former chairman of India's Atomic Energy Commission made the surprise announcement in a speech over the weekend, the Press Trust of India news agency reported on Sunday.

India has reportedly been trying to build its own nuclear submarine, code-named the Advanced Technology Vessel, since the 1970s, but has struggled to produce a suitable nuclear reactor. While the efforts have been widely reported, they have never before been publicly confirmed.