Seoul, Apr 8 (IANS): North Korea might be preparing for its fourth nuclear test, a South Korean minister said Monday.

"I can only say that there are such signs (of North Korea's new nuclear test)," Unification Minister Ryoo Kihl-jae told lawmakers at the parliamentary meeting for diplomacy and unification.

His comments came after a lawmaker said there is a rise in movements of personnel and vehicles near the test complex at Punggye-ri, North Hamgyong province, citing unspecified sources.

The lawmaker asked whether the movement was the sign of the fourth nuclear test, reported Xinhua.

North Korea conducted its previous three nuclear tests at the Punggye-ri test site. The latest occurred Feb 12.

Ryoo noted that the question was related to "intelligence" matters and declining to share details.

Asked about the possibility of Seoul sending a special envoy to Pyongyang, the minister said that "now is not the stage" to end the political deadlock through dialogue and noted that the special envoy "does not seem to guarantee easing tensions" on the Korean peninsula.

Ryoo said that Seoul has had its door for dialogue with Pyongyang open, and added that Park Geun-hye government has never closed the door.

Regarding the entry ban to the Kaesong industrial complex, the minister said that 13 South Korean companies have stopped factory operation until now at Kaesong due to a lack of food and materials. He added that six more firms would halt their operations Monday.

North Korea barred the entry of South Korean workers and vehicles to the inter-Korean industrial zone at the border town of Kaesong for the sixth day, allowing only their departure from Kaesong.

The industrial park, launched in late 2004, is housing 123 South Korean companies that are employing some 54,000 North Korean workers.