The main opposition Democratic Party's top spokesperson Kwon Chil-seung attends a press conference at the National Assembly on June 7. (Yonhap)

The ruling People Power Party referred an opposition lawmaker to the parliamentary ethics committee Thursday for making insulting remarks about the captain of the warship Cheonan sunk in a 2010 North Korean attack.

Rep. Kwon Chil-seung, senior spokesperson of the main opposition Democratic Party, said earlier this week that the Cheonan's captain, Choi Won-il, knows no shame even after "killing all his subordinates," accusing him of failing to fend off the North Korean attack.

Kwon made the remarks after Choi demanded the Democratic Party withdraw its decision to appoint a left-leaning civic leader, who had said he does not believe the North was responsible for the Cheonan's sinking, to head the party's innovation committee.

"What face does he have to say that?" Kwon said. "The captain is not supposed to disembark from the vessel. It is ridiculous (for him to say that) after killing all his subordinates."

The Cheonan sank in waters near the western sea border in March 2010, killing 46 sailors. An international investigation team concluded the vessel went down after a North Korean torpedo attack, but some left-leaning critics had raised questions about the conclusion.

On Wednesday, Kwon apologized for his remarks.

"I would like to express my deepest regrets to all those who have been hurt, including the families of the Cheonan naval ship sinking victims, for using inappropriate expressions as a party spokesperson," he said in a press conference.

On Thursday, Kwon also plans to meet with Choi and apologize.

The People Power Party is demanding Kwon step down as spokesperson and give up his seat in parliament. Ruling party lawmakers also urged opposition leader Lee Jae-myung to take responsibility. (Yonhap)