(Changes start of investigation to Wednesday from Monday in 2nd paragraph)
* Arrest warrant out for daughter of Choi Soon-sil
* Special prosecutors raid NPS, health ministry office
* Investigation linked to merger of Samsung Group affiliates
* Some 30 lawmakers break away from ruling Saenuri Party
By Ju-min Park
SEOUL, Dec 21 (Reuters) - South Korea on Wednesday issued an arrest warrant for a daughter of the woman at the centre of President Park Geun-hye's corruption scandal and investigators raided the National Pension Service over possible links to the scandal.
A special prosecutor's investigation started on Wednesday into the influence-peddling scandal that threatens to make Park, 64, the first democratically-elected leader to leave office early in disgrace. Parliament has voted to impeach Park, a decision that must be confirmed or overturned by the Constitutional Court.
A court issued an arrest warrant on Wednesday for Chung Yoo-ra, the 20-year-old daughter of Choi Soon-sil, Park's long-time friend who is in custody and on trial for fraud and abuse of power.
Chung's lawyer has said she is in Germany, where she flew with her mother and child in September, according to media reports.
"We have Chung's arrest warrant on several charges including obstruction of justice and we plan to request the cooperation of German prosecutors based on these charges," Lee Kyu-chul, a spokesman for the special prosecutor's office, told a news conference.
Lee said authorities are working to invalidate Chung's South Korean passport and have asked German prosecutors for information on her whereabouts and financial assets.
Chung, an equestrian athlete who competed in the 2014 Asian Games and won a gold medal in a team competition, sparked public ire earlier this year when it emerged that she had received special treatment from the prestigious Ewha Womans University.
Her admission to the university was subsequently cancelled. She was also stripped of her high school diploma for fabrication of grades and attendance, according to the Seoul education office.
PENSION OFFICE RAIDED
Hours earlier, investigators raided the office of the world's third-largest pension fund, the National Pension Service (NPS), over possible links to the scandal.
The special prosecutor's office is looking into NPS' decision last year to back the $8 billion merger of two Samsung Group affiliates, which was criticised for strengthening the founder family's control of the group at the expense of other shareholders.
The NPS was a major shareholder of both companies.
Investigators are also examining whether Samsung's support of a business and foundations backed by Choi may have been connected to NPS' support of the deal, a prosecution official told Reuters, declining to be named because he was not authorised to speak with media.
An office at the Ministry of Health and Welfare, which administers the NPS, was also raided on Wednesday, a Ministry of Health and Welfare spokeswoman confirmed.
NPS and Samsung Group could not immediately be reached for comment.
NPS' backing of last year's merger of Samsung C&T Corp and Cheil Industries was seen as crucial to the deal winning shareholder approval. Last month, a different team of prosecutors raided offices of Samsung and the NPS.
Meanwhile, more than 30 lawmakers from Park's ruling Saenuri Party who supported the impeachment vote announced on Wednesday they plan to break from the party, a move that will undermine the party's position in the 300-member chamber.
The conservative Saenuri Party currently holds 128 seats.
Park's possible impeachment has upended politics in South Korea, where, if she leaves officer early, an election will be held in 60 days.
Park was stripped of her powers, which are now held by the country's prime minister.
(Additional reporting by Joyce Lee; Writing by Christine Kim; Editing by Tony Munroe and Michael Perry)