Quoting defence industry sources, TASS said the state-controlled United Aircraft Corporation was overseeing the project.

It said material was being shipped for the project and that work had begun on the cockpit of the bomber, known as the PAK DA.

"The final assembly of the entire machine should be complete in 2021," one of the sources told TASS.

Stealth bombers are designed to evade radar detection while carrying large amounts of weaponry.

Russian officials have revealed few details of the project, though last year Deputy Defence Minister Alexei Krivoruchko said aircraft maker Tupolev -- which is part of United Aircraft Corporation -- was in charge.

Reached by AFP, United Aircraft Corporation spokesman Sergei Loktionov declined to comment on the report. Tupolev also did not immediately reply to a request for comment.

Reports have said the plane will feature a flying wing design similar to US stealth bombers, fly at subsonic speeds and carry strategic cruise missiles and hypersonic weapons.

The US Air Force's B-2 stealth bombers are among the world's most feared aircraft.

China is working on its own long-range stealth bomber -- the Xian H-20 -- with the South China Morning Post reporting this month that it could make its first public appearance at an airshow in November.