World reaction
"Initial indications are that the first stage of the missile fell into the sea 165km (105 miles) west of Seoul, South Korea. The remaining stages were assessed to have failed and no debris fell on land. At no time were the missile or the resultant debris a threat," the North American Aerospace Defense Command (Norad) said in a statement.
Japan reported similar details.
"At approximately 7:40 a.m. we confirmed that a certain flying object was launched from North Korea and fell after flying for just over a minute. There was no impact on Japanese territory," Japanese Defence Minister Naoki Tanaka said.
South Korea said the rocket exploded into some 20 pieces and fell into the sea. "We are conducting a search operation to retrieve the fallen objects," a defence ministry official said.
Some five hours after the launch, North Korea confirmed it had been unsuccessful.
"The earth observation satellite failed to enter its preset orbit. Scientists, technicians and experts are now looking into the cause of the failure," state-run KCNA news agency said.
'Provocative action'
Kim Jong-un at the Workers' Party conference in Pyongyang on 11 April 2012 (Image via KCNA) Kim Jong-un inherited the North Korean leadership in December 2011
The US said that North Korea's behaviour was of concern to the global community.
"Despite the failure of its attempted missile launch, North Korea's provocative action threatens regional security, violates international law and contravenes its own recent commitments," a White House statement said.
Pyongyang agreed in February to a partial freeze in nuclear activities and a missile test moratorium in return for US food aid. But that deal was put on hold last month after the North announced its rocket launch plans.
Earlier this week reports also emerged from South Korea of a possible third nuclear test being planned by North Korea.
North Korea conducted a similar rocket launch in 2009. On that occasion US and South Korea analysts said the rocket failed to reach orbit - but North Korea said it was a success.
The failure of this launch could pose a challenge for Pyongyang, which is holding a week of high-profile events ahead of the formal celebrations to mark Kim Il-sung's birthday on Sunday.
The Workers' Party held a rare conference on Wednesday and the country's rubber-stamp parliament is due to meet on Friday.
Both meetings are seen as formalising the transition of power to young leader Kim Jong-un following the death of his father Kim Jong-il in December 2011.