The South African government has condemned as "unacceptable" the nuclear test carried out on Monday by North Korea.

"The possession of nuclear weapons does not create security, but rather diminishes it and constitutes a threat to all humanity," said the department of international relations and co-operation in a statement.

"We call upon the Democratic People's Republic of Korea to fully and verifiably terminate any nuclear weapons programme..."

It also urged North Korea to return to the treaty on the non-proliferation of nuclear weapons, sign and ratify the comprehensive nuclear-test-ban treaty, and place its nuclear facilities and materials under comprehensive International Atomic Energy Agency safeguards.

North Korea first tested a nuclear bomb in 2006. It was one kiloton. The bomb used in Monday's underground explosion was 10 to 20 kilotons, according to an Agence France Presse report.

The country insists that it needs nuclear weapons for self defence, despite worldwide pleas that it give up its nuclear programme in exchange for energy aid and security guarantees.