WASHINGTON, October 11 (RIA Novosti) - North Korea could have accumulated up to 60 kg of plutonium since the early 1990s, Robert Gallucci, a former chief U.S. negotiator with Pyongyang, told a seminar in Washington.

Gallucci, who now heads the Walsh School of Foreign Service at Georgetown University, said the reclusive communist state held six to seven kg of plutonium in the early 1990s, and could have accumulated another 50 kg at its Yongbyon facility since then.

Christopher Hill, Washington's chief nuclear envoy, voiced similar apprehensions in an interview with the Public Broadcasting Service (PBS) last Wednesday.

Commenting on the closure of North Korea's Yongbyon nuclear reactor, along with reprocessing and fuel fabrication facilities, he warned that although the facilities would not be able to produce further plutonium, that would not solve the issue of plutonium already produced, which he also estimated at 50 kg.

Hill said the quantity was enough for five or ten warheads, "depending on how big your bomb is."

The U.S. official said hopefully "we can get them to give up these 50 kilos of bomb-making equipment" next year.