Two senior North Korean officials, including one army colonel who specialized in espionage against the South, defected to South Korea in 2015, the Seoul government said on Monday.

News of the defections followed Friday's announcement by Seoul that 13 workers at a restaurant run by the North in an undisclosed third country had defected as a group, arriving in the South a day earlier.

On Monday, the South's Unification and Defense Ministries said a North Korean army colonel defected last year and had been granted political asylum. He had worked in the secretive General Reconnaissance Bureau, which is focused on espionage activities against the South.

An unnamed official told South Korea's Yonhap news agency that this was the highest-level military figure ever to have defected and the colonel specialized in anti-South espionage operations, adding that: "He is believed to have stated details about the bureau's operations against South Korea to the authorities here."

South Korean officials declined to comment on that or give further details.

The Unification Ministry, which handles North Korea issues, also said that a senior diplomat who was posted in an African country had defected to the South last year with his family.

The disclosures confirmed earlier reports in the South Korean media. The South Korean government's public acknowledgement of defections is unusual.

The main liberal opposition Minjoo Party on Monday accused the government of President Park Geun-hye of trying to influence conservative voter turnout ahead of Wednesday's parliamentary elections by announcing the defection of the restaurant workers last week.

Both ministries denied suggestions that Monday's revelations were made for domestic political reasons and said disclosing the defections was in the public interest.

The two Koreas have been fierce rivals since the 1950-53 Korean War. As of March this year, the number of North Koreans who have fled the country for the South was around 29,000, including 1,276 last year, with numbers declining since a 2009 peak.

The defection of a high-ranking officer in the General Reconnaissance Bureau would be a coup for Seoul. The North set up the bureau in 2009, consolidating several intelligence agencies to streamline operations aimed at the South.

Its head, General Kim Yong-chol, is accused by the South of being behind the 2010 torpedo attack against the South that sunk a navy ship and killed 46 sailors. The North denies any responsibility for the sinking.

The bureau is also known to operate an elite team of computer specialists working to infiltrate the networks of the South and other countries and to conduct cyber attacks against key institutions.