Seoul, Mar 28 (IANS): South Korea's Unification Ministry on Monday expressed concerns about the possibility of an accidental clash with North Korea along the countries' border, as Pyongyang is ratcheting up tensions with a series of major missile tests.

In a report to the National Assembly committee on foreign affairs and unification, the Ministry said it will stay alert to prevent the occurrence of "accidental clashes" in the inter-Korean border areas, including around the Northern Limit Line (NLL), the de facto maritime border, reports Yonhap News Agency.

The North test-fired an intercontinental ballistic missile on March 24, and speculation is rife that it may be gearing up for a nuclear test.

"(We) will establish a firm posture to respond to all (possible) situations," the Ministry said in the report for the parliamentary panel's plenary session.

During a press briefing earlier in the day, it stressed that South Korea is closely monitoring North Korea's activities in cooperation with the US amid signs of the secretive North repairing its nuclear testing site.

It urged Pyongyang to immediately cease all relevant activities and return to the negotiating table.

Informed sources here said earlier the North seems to be seeking to make a "shortcut" to a tunnel at its once-defunct nuclear testing site in Punggye-ri.

The move is seen as aimed at making speedy preparations for a seventh underground nuclear experiment.