North Korea on Saturday reacted angrily to criticism that it intentionally timed its second nuclear test to coincide with South Koreans mourning the death of former president Roh Moo-Hyun.
The North's leader Kim Jong-Il sent a message of condolence to Roh's relatives Monday, a few hours before the communist state took the world by surprise by conducting an atomic test.
"Our nuclear test was carried out as a measure to step up self-defensive nuclear deterrence ... and it had nothing to do with the tragedy in the South," said Uriminzokkiri, an official website of North Korea.
Conservatives in the South had attacked the North for acting maliciously.
The website said North Koreans were also mourning death of Roh, a liberal president who pursued reconciliation and met Kim at a 2007 summit. Roh threw himself off a clifftop a week ago after facing corruption allegations.
The website accused the South's conservative ruling Grand National Party of seeking to cover up its responsibility for Roh's death and divert public attention from Roh's death.
Roh's supporters say the former president fell victim to a politically motivated investigation.
Relations between the two Koreas have deteriorated since conservative President Lee Myung-Bak took over from Roh in February 2008.
Tensions over the North's nuclear programme have risen after the North fired a long-range rocket in April and conducted its nuclear test Monday, its second since October 2006.