In an official statement read by Foreign Minister Kim Sung-hwan at the presidential office Cheong Wa Dae, the Seoul government said Pyongyang "must be held duly accountable for" the launch, which South Korea, the United States and other regional powers believed to be a disguised test of the North's intercontinental ballistic missile technology.
More than four hours after the launch, in a rare admission of failure, North Korea's state media acknowledged that an earth observation satellite failed to enter its orbit. South Korean military officials said the rocket exploded mid-air just a few minutes after lift-off.
"North Korea launched a de facto long-range missile, which the North calls an 'application satellite,' at 07:39 on April 13 at a launch site located in Cholsan-gun, North Pyongan province, and it has been confirmed that the launch has failed," Kim said.
"The launch by North Korea is a clear violation of United Nations Security Council resolution 1874," Kim said, referring to a 2009 U.N. resolution that prohibits North Korea from conducting "any launch using ballistic missile technology."
The failed rocket launch is "a provocative act that threatens peace and security on the Korean Peninsula and in Northeast Asia," Kim said.
South Korea "strongly condemns that the new North Korean leadership pushed forward with the launch, disregarding the international community's unified call for withdrawal of the launch," the foreign minister said.
"North Korea must be held duly accountable for its actions."
Kim said the Seoul government is "considering comprehensive measures to respond effectively against North Korea's nuclear and missile threats, and will take countermeasures against the launch in close coordination with related countries and the international community."
South Korean officials said the United Nations Security Council will convene on Friday (New York time) to discuss what steps it will take following the North's launch.
A senior official at the foreign ministry called for a "firm" response from the U.N. council against North Korea's defiant launch.
"Regardless of its success or failure, we urge the U.N. Security Council to take firm and unified action against North Korea's launch of a long-range missile," said a senior official at Seoul's foreign ministry.
Also on Friday, Kim and U.S. Secretary of State Hillary Clinton talked by telephone and vowed to take "resolute" action against North Korea's launch, Seoul officials said.
In their 10-minute telephone conversation, Kim and Clinton agreed to forge close cooperation against the North's launch and refer the issue to the U.N. Security Council.
Kim and Clinton "shared the view that the international community should send a clear and strong message to North Korea," the official said on the condition of anonymity, adding they also agreed to take "resolute" action against Pyongyang.
After his telephone conversation with Clinton, Kim met with U.S. Ambassador to South Korea Sung Kim and U.S. Army Gen. James Thurman, the commander of U.S. Forces Korea.
At the meeting, Kim and the U.S. ambassador said they were not surprised by the failure of North Korea's rocket launch.
"Our judgment is that it failed," Kim told the U.S. ambassador.
"It's not surprising," the U.S. envoy replied. The foreign minister responded, "Yes, I'm not surprised."
"I just had a telephone conversation with Secretary of State Clinton," the minister said. "Her judgment was also that they have failed."
The U.S. ambassador said, "I think it will take some time to figure out how it failed."
Seoul's defense ministry said the North's rocket exploded in mid-air just a few minutes after its launch and disintegrated into some 20 pieces. The debris fell into the Yellow Sea off South Korea's west coast.
South Korea's Navy is conducting a search operation to retrieve the fallen debris, ministry officials said.