South Korea's National Assembly is set to focus its efforts on the last session of questioning in regards to President Park Geun-hye's alleged corruption scandal slated for later this week, as key figures are expected to appear for the parliamentary probe, sources said Sunday.

Former presidential secretary Woo Byung-woo, who had been dodging the summons request, is among the figures who will join the session.

The probe slated for Thursday is especially crucial as the parliament's special committee looking into the case has been making little progress in finding details behind the scandal at the previous sessions.

Park was impeached on Dec. 9 over the influence-peddling scandal involving her confidante Choi Soon-sil, who is thought to have exerted influence on state affairs and profited from her close ties to the chief executive. Choi's key acquaintances, as well as other presidential staff members and business tycoons, have been summoned by the National Assembly for questioning.

On Thursday, 18 figures are expected to be summoned, including Woo, who is charged with delinquency of duties for remaining silent while being aware of Choi's interference in state affairs.

Choi was also summoned by the parliament, but her attendance remains uncertain. The confidante has been refusing to attend, citing her fragile health. Choi has been in custody since last month.

Amid the rising criticism over the investigation on the influence-peddling scandal that has failed to secure testimonies from Choi, the parliamentary committee earlier said it would seek to hold a separate session at her cell, tentatively on Friday.

The committee will also seek to hold an on-site visit to the presidential office this week, which ended in vain last week as Cheong Wa Dae refused to accept the investigation, citing security issues. (Yonhap)