(Updates with rally, paragraph 13)
By Jack Kim
SEOUL, Dec 31 (Reuters) - A South Korean court issued an arrest warrant on Saturday for the head of the national pension fund, the world's third largest, in a corruption scandal that has led to President Park Geun-hye's impeachment, an official said.
A special prosecutor probing the wide-reaching scandal has sought the arrest of the National Pension Service (NPS) Chairman Moon Hyung-pyo on charges of abuse of power and perjury.
The Seoul Central District Court issued the warrant saying evidence supported the charges against Moon, an official at the court said, but did not provide further details.
The special prosecutor's office said on Thursday Moon had acknowledged that he had pressured the fund to approve an $8 billion merger between two Samsung Group units last year while he was Health and Welfare Minister.
He denied during a parliamentary hearing in November that he had exerted pressure on the NPS, which is run by the ministry, to back the merger. His lawyer in a court hearing on Friday about the warrant again denied Moon had presured the NPS, local media reported.
The merger last year of Samsung Group affiliates Cheil Industries Inc and Samsung C&T Corp has become central to the investigation of the scandal that led parliament to vote this month to impeach Park.
The merger has been criticised by some investors for strengthening the founding family's control of Samsung Group, South Korea's largest "chaebol", or conglomerate, at the expense of other shareholders.
The NPS, which had 545 trillion won ($451.78 billion) under management at the end of September and was a major shareholder in the two Samsung affiliates, voted in favour of the merger without calling in an external committee that sometimes advises it on difficult votes.
The special prosecutor's office is probing whether Samsung's support for a business and foundations backed by the president's friend, Choi Soon-sil, at the centre of the corruption scandal, may have been connected to the NPS support for the merger.
Park, 64, is accused of colluding with Choi to pressure big businesses to make contributions to non-profit foundations backing presidential initiatives.
She has denied wrongdoing but apologised for carelessness in her ties with Choi, a friend for four decades, who has also denied wrongdoing. Choi is in detention while on trial.
Park's impeachment is being reviewed by the Constitutional Court, which has 180 days from the Dec. 9 parliament impeachment vote, to uphold or overturn it and reinstate the leader.
A large crowd gathered in central Seoul for a 10th consecutive weekend rally to demand that Park step down immediately. They listened to speeches and music ahead of a march towards the presidential Blue House. (Reporting by Jack Kim; Editing by Lisa Shumaker and Gareth Jones)