North Korea often test-fires missiles at times of regional tension
North Korea has fired two more missiles, hours after the UN Security Council unanimously condemned its nuclear test, South Korean reports say.
The communist state fired two short-range missiles off an east-coast base, South Korea's Yonhap news agency reported, citing an official.
The move came as UN diplomats began work on a resolution to punish North Korea for its underground nuclear test.
Diplomats said they were seeking "tough measures", including further sanctions.
At least three missile tests accompanied Monday's nuclear test. Those on Tuesday involved one ground-to-ship missile and one ground-to-air missile, Yonhap said.
Earlier, North Korea, in a statement carried by its official news agency KCNA, said it was clear America's "hostile policy" towards it had not changed.
"Our army and people are fully ready for battle... against any reckless US attempt for a pre-emptive attack," it said in a piece criticising US moves to relocate its fighter jets.
South Korea, meanwhile, announced it would become a full member of a US-led initiative aimed at controlling trafficking in weapons of mass destruction, despite warnings from Pyongyang.
Late on Monday US President Barack Obama spoke to the leaders of both Japan and South Korea to assure them of America's commitment to security in north-east Asia.
The conversations followed an emergency session of the UN Security Council, where members voiced strong opposition to the test and condemned it.
Russia's UN envoy told reporters the nuclear test was a clear violation of UN Resolution 1718. That resolution imposed sanctions on North Korea after its first nuclear test, in October 2006.
The US ambassador to the UN, Susan Rice, said America wanted "strong measures" when it starts work on the new resolution.
"The US thinks that this is a grave violation of international law and a threat to regional and international peace and security," she said.
The UK's ambassador to the UN, Sir John Sawers, explained that the Council had decided to act in two stages, first issuing a statement "strongly condemning and opposing what the North Koreans have done by carrying out this second nuclear test".
"And we decided to start work immediately on a further Security Council resolution in order to uphold the international peace and security in the region," he added.
The question, says the BBC's Laura Trevelyan at the UN, is what kind of sanctions against North Korea can be agreed and whether they will persuade it to rejoin talks on ending its nuclear programme.
On Tuesday, Asian and European foreign ministers attending the two-day biennial Asem Summit in Hanoi issued a statement condemning the test and calling for an immediate return to talks.
The issue was also expected to dominate talks between Chinese and South Korean defence ministers as they met in Beijing.
Oct 2006 - North Korea conducts an underground nuclear test
Feb 2007 - North Korea agrees to close its main nuclear reactor in exchange for fuel aid
June 2007 - North Korea shuts its main Yongbyon reactor
June 2008 - North Korea makes its long-awaited declaration of nuclear assets
Oct 2008 - The US removes North Korea from its list of countries which sponsor terrorism
Dec 2008 - Pyongyang slows work to dismantle its nuclear programme after a US decision to suspend energy aid
Jan 2009 - The North says it is scrapping all military and political deals with the South, accusing it of "hostile intent"
April 2009 - Pyongyang launches a rocket carrying what it says is a communications satellite
25 May 2009 - North Korea conducts a second nuclear test
Seoul announced early on Tuesday that it would delay no longer in joining the PSI - a US-led non-proliferation campaign involving searching ships carrying suspect cargo, aimed at stopping the trafficking of weapons of mass destruction.
North Korea has repeatedly warned that the South's participation in the PSI would be tantamount to a declaration of war.
Joining the PSI "is a natural obligation", South Korean Foreign Minister Yu Myung-hwan said, quoted by Yonhap. "It will help control North Korea's development of dangerous material."
Monday's blast, which seismologists said had the power of a 4.5 magnitude earthquake, appears to have been much more powerful than North Korea's first nuclear test.
Defence officials in Russia say it was an explosion of up to 20 kilotons, making it comparable to the American bombs that flattened Hiroshima and Nagasaki in 1945.
The test came after North Korea walked away from long-running disarmament talks.
It agreed in February 2007 to abandon its nuclear ambitions in return for aid and diplomatic concessions.
But the negotiations stalled as it accused its negotiating partners - the US, South Korea, Japan, China and Russia - of failing to meet agreed obligations.