The United States has called North Korea's missile programs a global threat after the communist nation reportedly fired two missiles near its border with China.

Media reports differed on whether the missiles were launched as a test or by mistake. However, a White House spokesman, Scott McClellan, said the launches were similar to previous tests carried out by North Korea.

Pyongyang has offered no public information about the missile launches.

Meanwhile, the chief U.S. negotiator at stalled nuclear talks, Christopher Hill, says North Korea is blocking progress in the negotiations.

Earlier Wednesday, a senior North Korean diplomat, Li Gun, repeated Pyongyang's refusal to return to talks over its nuclear program until the United States lifts financial sanctions on North Korean assets.