North Korea's military celebrated the controversial nuclear and missile tests
North Korea is reported to have fired another missile, despite US warnings it would "pay a price" for nuclear and missile tests in recent days.
The launch of the missile coincides with efforts to secure a UN Security Council resolution condemning the country's nuclear programme.
Washington says it is seeking a "quick and unified response" to the tests.
Earlier on Tuesday North Korea conducted an underground nuclear test and fired two short-range missiles.
The Yonhap news agency said the short-range missile was fired off North Korea's east coast, citing an unnamed South Korean government source.
Washington is calling for a quick and unified response by the international community that will make it clear to North Korea that there are consequences for its actions.
Diplomats from the five permanent Security Council member countries plus Japan and South Korea met behind closed doors to discuss a new resolution.
The US ambassador to the UN, Susan Rice, said after the meeting that a "good start" had been made but the discussions would take "some time".
"We are thinking through complicated issues that require very careful consideration," she said.
US Secretary of State Hillary Clinton spoke earlier to Russia's Foreign Minister Sergei Lavrov, as well her counterparts from China, South Korea, Japan and Australia.
The Obama administration said it was pleased with the decisive reaction so far, especially from Russia and China.
But US State Department spokesman Ian Kelly also indicated it was not too late for North Korea.
Mr Kelly said the door was still open to resume long-running six-party talks and that the US was looking at a "whole range of options".
It is a sign of the delicate balance required to handle the reclusive country, the BBC's State Department correspondent Kim Ghattas reports from Washington.
China shares a border with North Korea and worries about pushing Pyongyang too far, so it is unclear what sort of measures might be taken now and how North Korea would respond, our correspondent adds.
One option would involve enforcing sanctions already in place and to start inspecting shipments in and out of North Korea for the first time.
Ms Rice said earlier that international pressure on North Korea would increase, until it realised the tests had left it "further isolated and further debilitated".
She said the international community would not "throw up our hands and let them pursue this path" and that North Korea would "pay a price for their action".
Earlier, the Security Council unanimously condemned the tests.
Diplomats said they were seeking "tough measures", including further sanctions.
The Communist state responded by firing two short-range missiles off an east-coast base hours later, South Korea's Yonhap news agency reported, citing an official.
The agency said the tests involved one ground-to-ship missile and one ground-to-air missile.
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.
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
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.
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.