(LEAD) N.K. presumed to be holding 280 kg of highly enriched uranium: expert

(ATTN: UPDATES with reaction from foreign minister in last 3 paras)

SEOUL, Feb. 9 (Yonhap) -- North Korea is presumed to possess around 280 kilograms of highly enriched uranium, which, combined with the country's plutonium stockpile, is enough to make