South Korea has detected a "massive" deployment of North Korean troops and arms near the capital Pyongyang, Seoul's defence ministry said Tuesday.
The large number of soldiers, armoured vehicles and artillery have been stationed near the communist state's capital since July 12, the ministry said in a report to parliament.
The deployment appears to be related to political events such as a meeting of key communist party delegates next month and the party's 65th anniversary on October 10, a ministry spokesman said.
"The massive deployment of troops could be designed to show their military power at home and abroad, or for security," he said.
North Korean leader Kim Jong-Il has not publicly appointed an eventual successor, but his youngest son, Kim Jong-Un, is widely believed to be being groomed to take over from his ailing 68-year-old father.
Some analysts say Kim Jong-Il will probably designate the son as his political heir at the September meeting, the third such gathering since the communist state was founded in 1948.
It is seen as the most important party event since 1980, when a convention of all-party members made public Kim Jong-Il's status as the eventual successor to his father, and founding president, Kim Il-Sung.
Kim Jong-II took over from his father in 1994 in the communist world's only dynastic succession.
South Korea's spy chief said in June that the leader's poor health was driving him to speed up preparations for a handover and that Jong-Un was taking a greater role in policymaking and often accompanied his father on inspection tours.