South Korea expressed regret on Sunday over what it called a "reckless" rocket launch by North Korea.
"The government cannot but express disappointment and regret over North Korea's reckless act of firing a long-range rocket, which poses a serious threat to security on the Korean peninsula and the world," said presidential spokesman Lee Dong-Kwan.
"The government will deal firmly and resolutely with North Korea's provocative act," said Lee, without giving immediate details of Seoul's response.
The spokesman said Seoul would also be "patient" in waiting for its communist neighbour to change its attitude.
The North had said it intended to launch an experimental communications satellite -- an exercise that critics said would be a disguised ballistic missile test.
Yonhap news agency quoted an unidentified Seoul official as confirming the rocket had carried a satellite. There was no immediate information on whether it had been successfully put into orbit.
Seoul said the launch took place at 11:30:15 (0230 GMT plus 15 seconds).
The rocket appears to have crossed over Japan and reached airspace over the Pacific Ocean, the Japanese government said in an email alert.
North Korea had said the rocket's first stage would fall in the sea 75 kilometres (about 50 miles) west of Japan, and the second stage would plunge into the Pacific.