North Korea will likely launch missiles and large-scale military drills for its military foundation day later this month, South Korea's defense ministry said Monday.

The North is also capable of conducting a nuclear test with little preparation at its nuke test site at Punggye-ri in North Korea's northeast North Hamgyong province, the ministry added.

Pyongyang conducted nuclear tests, in 2006, 2009 and 2013.

The move comes as Seoul and Washington are to wrap up a months-long joint military exercise on Friday, which the North has claimed is a rehearsal for an invasion of the North.

On April 3, North Korea test-fired short-range missiles presumed to be KN-02 ground-to-ship missiles into the Yellow Sea following the test-firing of a single projectile the day prior.

The North is known to have designated a no-fly and no-sail zone in the East Sea earlier this month, a sign of an immediate missile launch.

In a report to the National Assembly, the ministry said it will closely watch movement in the North on April 25, the country's military foundation day, noting that North Korea seems to have raised its guard after Seoul activists resumed the launch of anti-Pyongyang leaflets to the North.

"It seemed that North Korea has increased military exercises involving artillery and guns at areas near where Seoul activists fly balloons carrying such leaflets," the report showed.

Leading activists have recently resumed a cross-border campaign to launch leaflets and DVDs of the U.S. movie "The Interview," a comedy about a fictional plot to assassinate North Korean leader Kim Jong-un.

The defense ministry said that the North has raised its combat readiness by deploying a patrol ship and other artillery in waters off its northwest coast, raising concerns of a possible accidental military clash between the two Koreas.

The two Koreas fought bloody battles in 1999, 2002 and 2009 near the Northern Limit Line in the West Sea, the de-facto inter-Korean maritime border.

Pyongyang does not acknowledge the border, which was drawn unilaterally by the U.S.-led United Nations Command when the 1950-53 Korean War ended with a ceasefire. The North has long demanded that the line be drawn farther south. (Yonhap)