North Korea's neighbours have strongly condemned the rocket launch
North Korea has defied international warnings and gone ahead with a controversial rocket launch.
State media said a satellite had been put into orbit and was transmitting data and revolutionary songs.
But there has been no independent confirmation so far. The US, Japan and South Korea suspect the launch was a cover for a long-range missile test.
They strongly condemned the launch. The US president told Pyongyang to "refrain from further provocative actions".
"North Korea broke the rules once more by testing a rocket that could be used for a long-range missile," Mr Obama told a crowd in the Czech capital, Prague.
"This provocation underscores the need for action - not just this afternoon at the UN Security Council, but in our determination to prevent the spread of these weapons."
Obama condemns North Korea launch
Japan called the move "extremely regrettable", while South Korea said it constituted a clear breach of a United Nations resolution.
UN Secretary General Ban Ki-moon said North Korea's actions were not conducive to regional stability, as did the European Union.
China and Russia both called on all sides to act with restraint, while the UK urged North Korea to immediately halt all missile-related activity.
The UN Security Council has approved a Japanese request for an emergency session.
Washington, Tokyo and Seoul regard the launch as a clear violation of Security Council resolution 1718 adopted in October 2006, which bans North Korea from carrying out ballistic missile activity.
North Korea announced several weeks ago that it planned to send what it called an "experimental communications satellite" into space from the Musudan-ri launch site in the north-east.
The three-stage rocket blasted off just before midday local time, within a pre-announced launch window.
It flew over Japan towards the Pacific, with two booster stages dropping into the ocean to the east and west of Japan, Tokyo said.
Japan said it had not tried to intercept the rocket. It had indicated it would do so if the rocket threatened its territory.
North Korea says the launch is part of what it calls peaceful space development.
"Our scientists and engineers have succeeded in sending satellite 'Kwangmyongsong-2' into orbit by way of carrier rocket 'Unha-2'," state news agency KCNA reported.
It added that it was transmitting data and the "Song of General Kim Il-sung" and "Song of General Kim Jong-il" - references to the late founder of North Korea and his son, the current leader.
In a previous satellite launch attempt in 1998, North Korea said it was sending up a device that would orbit the world transmitting revolutionary melodies.
It claimed this was also successful but the launch is believed to have been a failure as no trace of the satellite was ever found.
Earlier on Sunday, an unidentified South Korean official told Yonhap news agency that the rocket did appear to be carrying a satellite.
If confirmed, North Korea will see this as a major propaganda victory, says the BBC's John Sudworth in Seoul.
A White House spokesman said there would be an assessment by defence and intelligence officials later in the day.
US within range?
But of more concern to Pyongyang's neighbours is the potential military use of the launch vehicle, our correspondent says.
They believe the real aim of the launch was to test long-range missile technology; specifically the Taepodong-2.
They believe it could put parts of the US within the communist nation's military reach.
North Korea first tested a Taepodong-2 in July 2006. It failed less than a minute after lift-off.
Three months later, Pyongyang carried out a nuclear test.
International talks involving the US, South Korea, Japan, Russia and China on an aid-for-nuclear disarmament deal are currently stalled.