North Korea has said it is no longer observing a self-imposed moratorium on long-range missile testing which has been in place since 1999.
N Korea has not launched long-range missiles since 1998
The statement, which was issued late on Wednesday, was played down by the US and Japanese governments.
A Japanese foreign ministry spokesman said he thought North Korea might be trying to raise the stakes ahead of a possible resumption of nuclear talks.
The North last launched a missile that grabbed the world's attention in 2003.
The statement, in a commentary carried by state news agency KCNA, said the moratorium on long-term missile testing was announced while US-North Korean dialogue was under way, but that since that dialogue was now suspended, so was the test ban.
"We are not bound to the moratorium on the missile launch at present," it said.
Map shows range of Taepodong 1 missile, flown over Japan in 1998. Range 1,500-2,000 km, payload: 1,000 kg
Evidence that North Korea working on testing Taepodong 2. Range up to 8,000 km (could reach western US)
Evidence from Jane's Defence of a pair of new ballistic missiles - one sea-based
Other missiles: Scud-B: Range 300 km, payload 1,000 kg
Scud-C: Range 500 km, payload 7600-800 kg
Scud-D (Nodong): Range 1,000-1,300 km, payload: 700-1,000 kg
Japanese Foreign Ministry spokesman Akira Chiba said Tokyo did not expect North Korea to act on its threat.
"We are keeping our eye on the situation. We don't expect them to fire missiles," he said.
But US State Department spokesman Adam Ereli stressed that such a threat was "not helpful and doesn't serve a useful purpose. And I think it's not consistent with the spirit with the six-party talks".
North Korea abruptly withdrew from the six-nation talks last month, citing recent high-profile speeches by the Bush administration, including Secretary of State Condoleezza Rice's branding of Pyongyang as an "outpost of tyranny".
But US and Chinese negotiators are meeting in Seoul at the moment to discuss how to draw North Korea back to the talks.
North Korea last launched a high-profile missile test in March 2003, to coincide with the inauguration of South Korean President Roh Moo-hyun.
These were two short-range land-to-ship missiles fired into the Sea of Japan (East Sea).
It has not launched long-range missiles since 1998, when a Taepodong 1 missile flew over Japan.