There has been widespread international condemnation of North Korea's failed rocket launch.
The US and its allies said it was a provocative act that threatened regional security, while Russia, China and India urged all parties to show restraint.
United Nations chief Ban Ki-moon, meanwhile, termed the rocket launch "deplorable".
North Korea earlier confirmed that the launch of its long-range rocket had failed.
The country's state news agency said the satellite it planned to send into space had not entered orbit.
Some four hours after the rocket reportedly exploded over the Yellow Sea, North Korea said that "scientists, technicians and experts are now looking into the cause of the failure".
The United Nations Security Council is to hold an emergency meeting to discuss the development.
There has been strong reaction from the US and its allies in the region, who had considered the project to be a concealed ballistic missile test.
"North Korea is only further isolating itself by engaging in provocative acts, and is wasting its money on weapons and propaganda displays while the North Korean people go hungry," White House spokesman Jay Carney said.
South Korea's defence ministry said the rocket, which lifted off at 07.39am (11.39pm Thursday Irish time), "flew about one or two minutes before it exploded mid-air".
"We are keeping a close watch over the North for further provocative acts such as missile tests and a nuclear test," the ministry said, referring to fears the launch could be followed by North Korea's third atomic test.
South Korea's Foreign Minister Kim Sung-Hwan said the actions were a "clear breach of the UN resolution that prohibits any launch using ballistic missile technology. It is a provocative act threatening peace and security."
Japan's Chief Cabinet Secretary Osamu Fujimura also condemned the move.
"Even if it was a failure, it is a grave provocation to our country and other countries concerned and violates UN Security Council resolutions," he said.
In a statement, the UN's Ban Ki-moon said it "defies the firm and unanimous stance of the international community," while urging North Korea "not to undertake any further provocative action that will heighten tension in the region".
The North American Aerospace Command (NORAD) said that together with the US military's Northern Command it "detected and tracked a launch of the North Korean Taepodong-2 missile."
It said initial findings indicated the rocket's first stage fell into the sea 165km west of the South Korean capital, Seoul.
"The remaining stages were assessed to have failed and no debris fell on land," it said. "At no time were the missile or the resultant debris a threat."
The Group of Eight powers led criticism of the launch and said they would consider taking "appropriate actions" at the UN Security Council, which meets today.
