An extraordinary parliamentary session kicked off Friday, with rival parties deadlocked over a special bill aimed at uncovering the truth behind April's ferry sinking that left more than 300 people dead or missing.

The session, which is to run for 10 days until the start of the regular parliamentary session in September, was requested by the No. 1 opposition party, the New Politics Alliance for Democracy (NPAD), on Tuesday, just as the rival parties failed to pass the special bill through the previous parliamentary session that ended that day.

NPAD claimed the new extra session would allow the bill to be passed as soon as an agreement is reached with the ruling party, but critics argued the move was aimed at protecting three NPAD lawmakers accused of graft. In South Korea, lawmakers are immune from arrest while the parliament is in session.

The special bill calls for the creation of an ad hoc investigative committee, which would be tasked with determining the truth behind one of the country's deadliest maritime accidents.

The tragedy has become a political football in South Korea as critics argue that the government's initial failure to properly respond to the disaster contributed to the high death toll.

The bereaved families of the victims have demanded the investigative committee be given the right to investigate and indict, but the ruling party has refused to let that happen over concerns it could disturb the judicial system and the division of powers prescribed by the Constitution.

"If victims investigate perpetrators, that would break the principle that bans self-help, which is something that cannot be tolerated in a civilized society," Rep. Lee One-koo, the floor leader of the ruling party, said in a phone interview with Yonhap News Agency. (Yonhap)