Former President Park Geun-hye will deliver a message before being questioned by the prosecution this week over a string of corruption allegations, her lawyer said Monday.

"Park Geun-hye has prepared a message. She will deliver it as she heads to the prosecutors' office," her lawyer Son Bum-kyu said in a text message sent to reporters. He declined to elaborate. 

Park, the country's first democratically elected leader to be ousted, is set to undergo questioning at the Seoul Central District Prosecutors' Office on Tuesday morning.

The ex-president has been named a criminal suspect for allegedly abusing her power and colluding with her longtime friend Choi Soon-sil in extorting money from local conglomerates.

Park has so far rejected a direct investigation as the nation's president is immune from criminal prosecution. The Constitutional Court's decision to oust her earlier this month stripped her of the privilege.

Prosecutors are accelerating their preparation for the questioning which could continue until past midnight.

"It seems like the questioning will continue until late at night," a senior prosecution official said, asking not to be named. "We try to end interrogations before midnight, but we will have to see how it goes tomorrow."

The inquiry of Park will take place in the presence of one or two lawyers, he said.

Park will be the country's fourth former president to undergo questioning over criminal allegations, following Roh Tae-woo, Chun Doo-hwan and the late Roh Moo-hyun.

Roh Moo-hyun committed suicide in 2009 amid an investigation into allegations that his family members accepted illicit funds. (Yonhap)