Choi was indicted first and has been on trial for months while Park was protected by her presidential immunity before she was impeached. Prosecutors finally indicted Park in April and added bribery charges against Choi that the first investigation by prosecutors and a probe by independent counsel Park Young-soo had lacked the time to put together.

Park and Choi are charged with taking or demanding W43.3 billion in bribes from Samsung and demanding W8.9 billion in bribes from SK and W7 billion from Lotte. They are also suspected of extorting billions more from other conglomerates, most of which went into Choi's slush funds.

The objection came in Park's second pre-trial hearing, in which she pleaded not guilty to all 18 criminal charges against her. Park was not present at the hearing but entered the plea through her lawyers. The formal trial starts next Tuesday.

Ex-President Park Geun-hye on Tuesday objected to a court decision to make her stand trial alongside her fatal confidante Choi Soon-sil, who is charged on many of the same counts of extortion and soliciting bribes.

The Seoul Central District Court earlier said it will combine the two cases since many of the witnesses and documents entered in evidence are the same. At the time, Choi's lawyers read out a typically histrionic statement from their client objecting to the decision, saying she feels "unbearable shame" at having to stand trial next to Park and likening the prospect to "gouging out her own eyes."

Park's fresh objection on Tuesday argued that she is not an accomplice to Choi and should be tried separately on the bribery charges.

"Choi's trial has progressed significantly already and combining the two cases will lead to possible bias from the judges," Park's lawyer said. "We will be faced with serious limitations from the start."

In the face of a fairly solid case, the defense tactics throughout Park's impeachment trial and now at her criminal trial have been to filibuster and complain of an obscure conspiracy against their client.

The pre-trial hearing, which usually takes half an hour, dragged on for an hour as Park's lawyers wrangled with the judge.

The judge said, "A separate trial would lead to the same witnesses being summoned twice," but added he will decide on their objection by the day the formal trial begins.

The case involves an army of witnesses and could drag on for months. The full lists have not been submitted, but there is speculation that up to 200 witnesses could be summoned.

The court has until October to reach a ruling and proposed to hold four sessions a week, but already Park's lawyer Yoo Yeong-ha claimed this is impossible considering Park's health, though he did not elaborate. The court agreed to reduce the number of sessions to three a week.

The trial has been delayed because Park reneged on pledges to submit to questioning from prosecutors while she remained holed up at Cheong Wa Dae. That has had a knock-back effect on the trials of other Cheong Wa Dae officials and Choi’s cronies.

The trial of Samsung chief Lee Jae-yong for bribing Park and Choi is expected to be wrapped up by late June, but he is likely to be sentenced at the same time as Park.

