U.S. officials

“Eight U.S. officials are in Moscow for talks with Russia on missile defense.”

“similar underground blasts were carried out in 2006 and 2009 following long-range missile tests.”

“between 300 and 400 strategic nuclear warheads”

“U.S. officials said a nuclear test by North Korea is expected because similar underground blasts were carried out in 2006 and 2009 following long-range missile tests.”