Police arrest a student activist outside the presidential office in central Seoul, Jan. 6, after a group of members of the Korean University Progressive Union attempted to illegally enter the grounds, in this image captured from a YouTube broadcast. Yonhap

Police arrested 20 university students affiliated with a progressive group Saturday after they attempted to enter the presidential office in central Seoul, officials said.

The members of the Korean University Progressive Union were caught at the site for allegedly attempting to trespass on the presidential office compound by entering through its western gate and climbing over its fences, according to the officials.

Before the attempt, the students had staged a protest outside the compound, demanding a special probe into first lady Kim Keon Hee and a meeting with presidential officials.

Police plan to investigate the incident further to determine the students' exact motives, among other details.

On Friday, President Yoon Suk Yeol vetoed two opposition-led special investigation proposals, one of which involves allegations against the first lady.

Kim has been accused of involvement in manipulating the stock prices of Deutsch Motors, a BMW car dealer in South Korea, between 2009 and 2012. She has denied the allegations. (Yonhap)