North Korea appears ready to conduct its fourth nuclear test, but no imminent signs have been detected at its main site on its northeastern tip, South Korea's defense chief said Monday.

During a parliamentary interpellation session, Kim Kwan-jin said Pyongyang has prepared for an underground nuclear test at the Punggye-ri site, which was used for the third atomic test a year ago, and has taken "initial steps" for a missile launch at its northwest test site in Tongchang-ri.

"These things (the nuclear test and the missile launch) depend on the decision by the North Korean leadership. As seen in the past, the long-range missile test and the nuclear test are connected to each other," Kim told lawmakers. "We are closely watching (the North Korean military) to prepare against any provocations."

The communist state is known to have tested an engine for its KN-08 long-range missile just before last year's atomic test, which is seen as efforts to master the technology to build a nuclear-tipped intercontinental ballistic missile.

According to the National Intelligence Service in October, Pyongyang is believed to have conducted several missile engine tests at the Tongchang-ri site last year and has been renovating the test facility since May 2013.

Last month, 38 North, a website specializing in North Korea-related news run by the U.S. Korea Institute of Johns Hopkins University, said a possible test of a rocket engine used by the KN-08 took place between late December 2013 and early January, citing satellite images. 

During the interpellation session, meanwhile, opposition lawmakers grilled the defense chief over allegations that he had been briefed about the cyber command's posting of political writings ahead of the 2012 presidential election.

Rep. Jin Sung-joon of the Democratic Party earlier claimed that Kim had been aware of the cyber command's online smear campaign activities, including posting writings critical of the then opposition camp, citing a senior official from the defense ministry's investigation team in charge of the probe into the unit.

Kim denied receiving briefings on the cyber command's online smear campaign, saying the reports were on general cyber attacks and psychological propaganda activities by North Korea.

"I received reports on North Korea's cyber attacks and a variety of propaganda and malicious slandering," Kim said. "But political writings are not subject to briefing."

Kim stressed that he repeatedly ordered soldiers to stay political neutral during the election campaign. (Yonhap)