UPDATE 1-South Korea Reveals Defection Last Year of Two N.Korea Officials

* News follows last week's defection of 13 restaurant workers

* Group from restaurant appears to have been working in China

* S.Korea opposition accuses govt of opportunism ahead of election (Adds Chinese comment on 13 North Koreans)

By Jack Kim and Ben Blanchard

SEOUL/BEIJING, April 11 (Reuters) - Two senior North Korean officials, including an army colonel specialising in espionage against the South, defected to South Korea last year, the Seoul government said on Monday.

News of the defections followed a South Korean announcement on Friday that 13 workers at a restaurant run by the North in an unidentified country had defected, a case it described as unprecedented, arriving in the South a day earlier.

South Korea did not say where the 13 had worked. China said on Monday that 13 North Koreans had been there and had left lawfully. It did not say if they were the same group.

The South's Unification and Defence Ministries said on Monday 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.

South Korea's 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 defection of a high-ranking officer in the General Reconnaissance Bureau is 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 a 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.

South Korea's Yonhap news agency said the North Korean colonel specialised in anti-South espionage operations before defecting and had divulged the nature of his work to South Korean authorities.

South Korean officials declined to comment.

News of the defections come after a period of tension on the Korean peninsula following the North's fourth nuclear test in January and a long-range rocket launch the next month.

'VALID PASSPORTS'

The South Korean government's public acknowledgement of defections is unusual.

The main liberal opposition Minjoo Party on Monday accused the government of conservative 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.

China is North Korea's main ally and is known for sending defectors back to the North, so South Korean media reports that restaurant workers had been there initially raised some surprise.

Asked about the workers on Monday, a Chinese foreign ministry spokesman said it had received a report about a group of 13 North Koreans in China who had gone missing.

"After an investigation, (we found) the 13 North Koreans used valid passports to leave the country normally in the early hours of April 6," Chinese foreign ministry spokesman Lu Kang told a regular briefing, without saying where they had gone.

"What needs to be stressed is that these people had valid identity documents and legally came to the country, not North Koreans who have entered illegally."

South Korea's Joongang Ilbo newspaper said the 13 worked at a restaurant in the Chinese city of Ningbo until around Tuesday last week when they disappeared, quoting a Chinese worker at the Ryugyong Korean Restaurant.

Calls to the restaurant seeking comment went unanswered.

South Korean media said the 13 left China and travelled to a Southeast Asian country before being flown to South Korea, citing unidentified government sources.

The South's Unification Ministry declined to comment on where the North Koreans had been before arriving in South Korea.

The two Koreas have been fierce rivals since the 1950-53 Koran War and about 29,000 people had fled North Korea and arrived in the South, since then, including 1,276 last year. (Additional reporting by Ju-min Park and Megha Rajagopalan; Editing by Tony Munroe, Robert Birsel)