The ruling and main opposition parties again failed Sunday to narrow their differences on a parliamentary probe into the spy agency's alleged involvement in last year's presidential election, only agreeing to jointly receive a report from the agency.

The agreement took place at a special meeting between the leaders of the ruling Saenuri Party and the main opposition Democratic Party (DP).

"The sides agreed their leaders will continue to hold discussions on which witnesses will be summoned after receiving a report from the National Intelligence Service (NIS) tomorrow,"

ruling and opposition party officials said shortly after Sunday's meeting between their floor leaders.

The rival parties have agreed to stage a parliamentary probe into the NIS' alleged meddling in last year's presidential election, but they have remained at odds on how to ensure compliance from two key figures in the proposed investigation -- former NIS chief Won Sei-hoon and former Seoul police chief Kim Yong-pan.

The DP demands the parliamentary investigation committee issue an advance order that the two comply unconditionally with the summons, while the ruling party says the demand is unacceptable because a compliance order can only be issued when witnesses snub a summons without justifiable reasons.

The main opposition party has been staging street protests since last week, and on Saturday it proposed a meeting with President Park Geun-hye herself for talks on ending the political impasse.

The president and her office have yet to respond, while a senior ruling party official speaking on condition of anonymity said the political deadlock should, and can only be resolved, through dialogue between the political parties, apparently leading to Sunday's meeting between their leaders. (Yonhap News)