About 300 people were detained on Thursday as police and protesters clashed in several Seoul areas after a mass rally to mark the 68th Liberation Day.

Thousands of activists and politicians took to the streets demanding President Park Geun-hye apologize for the National Intelligence Service’s alleged interference in last year’s presidential election, and engage North Korea more actively.

Police fired water cannons to disperse demonstrators who illegally occupied roads while marching through the city center.

On Wednesday night, civic, labor and student groups organized the seventh candle-lit rally in front of the City Hall against the intelligence agency.

Organizers claimed about 40,000 people joined the demonstration while the police put the number at about 7,500.

The first candlelight vigil took place in June with a few thousand, yet the number of participants gradually increased to tens of thousands, according to the civic groups.

Leaders of the opposition Democratic Party and some minor opposition parties also joined the 6th demonstration earlier this month.

Former spy chief Won Sei-hoon has been indicted over his role in the NIS’ alleged attempt to sway public opinion in favor of the ruling party through an online smear campaign during last year’s presidential election.

Former Seoul police chief Kim Yong-pan has also been charged in connection with the alleged attempt to whitewash the police investigation into the case.

The parliamentary probe started in July to uncover the incident. The National Assembly issued an order of accompaniment on Wednesday to the two former chiefs to attend the public hearing as they refused to appear at the previous hearing without due cause.

The current protests are the biggest since the anti-U.S. beef candlelight rallies in 2008, which triggered the first major crisis of the former Lee Myung-bak administration during his first year in office.

As the anti-NIS protests were poised to combine with resistance to a recent proposal to, in effect, increase the tax burden on the middle-class, President Park Geun-hye this week modified the plan.

By Lee Hyun-jeong (rene@heraldcorp.com)