Russia has agreed to write off 90 percent of the 11-billion-U.S.-dollar debt owed by the Democratic People's Republic of Korea (DPRK) to the former Soviet Union, Russian Finance Ministry said Tuesday.

An agreement on the restructuring of the debt was signed on Monday in Moscow, deputy finance minister Sergei Storchak told reporters.

DPRK owed former Soviet Union 11 billion dollars since the 1950s. Russia claims to be a legal successor of the Soviet Union which has built 70 plants and factories in DPRK and supplied the country with energy on subsidized prices.

Moscow and Pyongyang have been negotiating the debt issue for four years without finding a mutually acceptable solution, said the Russian Finance Ministry.

Under the newly-reached agreement, Russia decided to write off 90 percent of the debt and offered to restructure the remaining part.

The remaining debt would be included into a "debt for assistance" exchange scheme as investment to be injected into Russia-DPRK joint projects in humanitarian areas and energy sector, said the ministry.