South Korean President Park Geun Hye's comments followed last week’s unexpected execution of an uncle of North Korean leader Kim Jong Un

South Korea “must strengthen its security posture” against potential provocations from the North, President Park Geun Hye said Monday.

“The political and security situation has turned very grave,” Ms. Park told journalists before heading to a meeting with top security officials.

“The government, military and police should keep an even closer guard in case of possible contingencies from the North,” she said.

Her comments followed last week’s unexpected execution of an uncle of North Korean leader Kim Jong Un, previously considered a powerful ally and mentor of the young leader, but convicted of plotting a coup.

Analysts have said the move may have been an attempt by Mr. Kim to strengthen his grip on power, which he took two years ago on the death of his father and predecessor Kim Jong Il.

Over the weekend, Mr. Kim appeared in public apparently relaxed, visiting a military institute and a ski resort under construction.

The North Korean leader was expected to attend a ceremony later Monday at the Pyongyang mausoleum on the eve of the second anniversary of his father’s death.

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