U-S intelligence agencies are watching for signs that North Korea may conduct a flight test of a ballistic missile capable of hitting the United States.
U-S officials say Washington is closely watching North Korea's long-range missile program and the possibility that Pyongyang could launch a test of its Taepo Dong Two missile.
Since 1999, North Korea has observed a self-imposed moratorium on long-range missile test flights. But Pyongyang has recently linked the moratorium to progress in talks with Washington.
Those talks have been recently complicated by what the United States says was a North Korean acknowledgment that it was pressing ahead with a nuclear weapons program.
Russia on Thursday echoed U-S concerns, saying it was disappointed by Pyongyang's response to Moscow's request for information, saying there was some ambiguity in the North Korean statements.
Earlier Thursday, North Korea declared it has the right to develop nuclear and other weapons of mass destruction, because of a U-S threat to its sovereignty.
The North Korean ambassador to Moscow, Pak Hui Chun, accused the United States of breaking agreements with his government, while he denied that North Korea has abandoned a 1994 pledge to give up its nuclear program. Meanwhile, the head of the Pentagon's missile defense agency Thursday said Washington needs speed up its purchase of advanced anti-missile rockets to counter threats from states like North Korea, Iraq, Iran and Libya.
Lieutenant General Ronald Kadish told reporters in Washington that the United States has only about 40 of its most advanced Patriot missiles to defend against short-range ballistic and cruise missiles. He said the Patriot missiles are being produced at a rate of only two a month.
The Patriot missiles would have a more immediate value as a defense against Iraqi missile attacks against nearby U-S forces in any new war over Saddam Hussein's suspected weapons programs.
North Korea has not publicly acknowledged that it has a nuclear weapons program. But a U-S envoy who visited Pyongyang this month said the North Koreans did admit to him that they have such a program.