SEOUL, May 12-- South Korea's defense ministry said Thursday that it has been carefully monitoring the nuclear test site of the Dmocratic People's Republic of Korea (DPRK).

"(The DPRK) has completed preparations (for a test) at the Punggye-ri test site. We are continuously monitoring the developments there," ministry spokesman Moon Sang-gyun told a press briefing.

He said Pyongyang remains "ready" to detonate another atomic device at any time.

Yonhap quoted a source familiar with the activities at the nuclear test site in the country's northwest saying that movements of workers and vehicles are still seen in recent satellite imagery, which is a sign that preparations for an underground nuclear experiment are continuing.

Pyongyang was expected to carry out its fifth nuclear test before the seventh congress of the ruling Workers' Party of Korea (WPK) that ended on Monday.

In his three-hour speech aired by the state TV on May 8, the top leader of DPRK Kim jong-un described the DPRK as a "responsible nuclear weapons state," saying Pyongyang will strive for world denuclearization and faithfully fulfill obligations of nuclear non-proliferation.

He also proposed the two sides on the Korean Peninsula hold talks at all levels so as to remove misunderstanding and distrust.

However, Seoul has turned down the rare olive branch from Pyongyang saying the proposal is merely a propaganda drive with no authenticity.

"They are only an expression of the DPRK's perception of the current reality and its position on it," the Unification Ministry's Spokesman Jeong Joon-hee has said.