North Korea claimed Thursday that it has arrested a South Korean-hired agent it strongly suggested was tasked with assassinating the country's absolute leader, Kim Jong Il.

The North's Ministry of State Security said in a statement it had arrested a North Korean on a "terrorist mission" ordered by a South Korean intelligence organization "to do harm to the top leader" of North Korea.

The statement, carried by the country's official Korean Central News Agency, did not mention Kim Jong Il by name, but South Korean Unification Ministry spokesman Kim Ho-nyeon said the North's state media has before used such wording to refer to him.

Kim of the Unification Ministry, which handles relations with the North, said he was in no position to confirm the report.

The National Intelligence Service — South Korea's main spy agency — said it was checking the claim.

The sensational allegation comes amid a serious worsening of relations between the divided Koreas as well as intense speculation about Kim's health since he reportedly suffered a stroke and had brain surgery in August.

The North has denied its 66-year-old leader was ever ill, churning out a slew of media reports and photographs depicting him as healthy and active.

The North's agency identified the arrested man's family name as Ri and said he was tasked with gathering information about Kim's movements.

"The organization sent him speech and acoustic sensing and pursuit devices for tracking the movement of the top leader and even violent poison in the end," said the statement, which was also read on North Korean state television.

Tensions on the Korean peninsula have run high since a pro-U.S., conservative government took office in Seoul in February with a pledge to take a tough line on the North.

Ties worsened earlier this month after the North restricted traffic at the countries' border, leading to the suspension of tours to the ancient North Korean city of Kaesong.