SEOUL, Nov. 10 (Xinhua) — Hundreds of thousands of South Koreans are expected to rally in South Korea during an upcoming weekend to demand President Park Geun-hye's resignation over scandal involving her longtime confidante and former aides.

A private association aiming to let President Park step down, which is composed of about 1,500 civic groups, announced a plan to hold a massive rally in a city hall square in central Seoul this Saturday.

It would be the third weekend protest since the scandal over the president's decades-long friend, Choi Soon-sil, came into focus last month. Choi, who has been placed under custody, is charged with meddling in state affairs behind the scenes and peddling undue influence for personal gains.

Police estimates 160,000-170,000 protesters would attend the rally. Organizers said at least 500,000 would turn out, according to Yonhap news agency report on Thursday. Last Saturday, about 200,000 marched in Seoul to demand the embattled president's resignation.

This Saturday, the Korean Confederation of Trade Unions, one of the country's two umbrella labor union groups, expected to bring at least 100,000 unionists and supporters to the square.

Voluntary participants, including couples, families and students as seen in last Saturday's protest, are expected to peak in number. Three main opposition party members vowed to join the rally.

President Park has made public apologies twice, the latest last Friday to accept a direct investigation into herself "if necessary," but the apologies seemed to have infuriated the already enraged public further as some people felt that the president refrained from frankly confessing to her sins.

Public doubts remained about whether prosecutors can proactively investigate the president's involvement as Park still retains the biggest power in the country.

Student unions, university professor groups and civic group activists have issued separate declarations nationwide to demand Park step down. Even a group of about 2,300 singers demanded Park's resignation earlier this week.

Park made a visit to the parliament on Tuesday, allowing lawmakers to select a new prime minister and let him form a coalition cabinet, but three main opposition parties refused to settle on the country's No.2 executive post amid growing calls for the president's resignation.

Public calls are surging for the president to distance herself from diplomatic and defense affairs as well as domestic matters as she already lost her credibility and qualification to govern the country.

Seoul's foreign ministry said President Park would not attend the Asia-Pacific leaders' meeting in Peru later this month on security concerns on the Korean Peninsula, sparking media speculation that Park was forced to skip the regional summit over the political scandal.

Scores of protesters gathered in front of the defense ministry's headquarters on Wednesday, protesting against the ongoing discussion between South Korea and Japan to sign a bilateral military intelligence-sharing pact on the Democratic People's Republic of Korea (DPRK).

The attempt to seal the hush-hush military accord was dropped in 2012 under former President Lee Myung-bak on public outcry over the closed-door deal without social consensus and parliamentary consultations.

Many South Koreans still see such a deal with Japan as unacceptable as Japanese leadership has yet to sincerely apologize for past militaristic histories.

The opposition parties said that if the defense ministry continues to push for the behind-the-scenes deal, they would propose the resignation of Defense Minister Han Min-koo.