Rod Blagojevich says he believes he has done nothing wrong
The attorney general of Illinois has filed a lawsuit asking the US state's top court declare Governor Rod Blagojevich "unfit to serve".
Mr Blagojevich was arrested on Tuesday for allegedly trying to "sell" Barack Obama's Illinois Senate seat.
He denies the charges but the perceived abuse of his role has led to calls for him to stand down.
Mr Obama, the US president-elect, has said he is "appalled and disappointed" by Mr Blagojevich's alleged actions.
"In light of his arrest in the filing of the criminal complaint, Governor Blagojevich can no longer fulfil his official duties with any legitimacy," said Illinois Attorney General Lisa Madigan, announcing her decision to file a complaint to the Illinois Supreme Court.
"I recognise that this is an extraordinary request, but these are extraordinary circumstances," she added.
On Tuesday, federal investigators, who had been working on a case against Mr Blagojevich for several years, charged him with a number of offences including soliciting a bribe.
The charges relate to a variety of corruption schemes in which the governor was allegedly involved, including so-called "pay to play" deals - the doling out of jobs, contracts and appointments in return for campaign contributions.
CHARGES AGAINST BLAGOJEVICH
Federal agents say Mr Blagojevich
Tried to obtain campaign contributions in exchange for official actions;
Tried to use state funds for the private purpose of inducing the Tribune Company to fire Chicago Tribune editorial board members critical of him;
Tried to obtain personal financial benefits for himself in return for his appointment of a US senator
The US Attorney's Office released a 76-page FBI affidavit on Tuesday detailing the charges against Mr Blagojevich, which includes transcripts of his telephone conversations intercepted by court-authorised wiretaps over several weeks.
In the conversations, the Democratic governor allegedly discussed offering Mr Obama's Senate seat in return for a well-paid position at a non-profit organisation or a group affiliated with trades unions, according to the affidavit.
As governor, Mr Blagojevich has the sole authority to pick Mr Obama's temporary successor as senator until an election is held.
In the transcripts, on 3 November Mr Blagojevich said the seat was a "[expletive] valuable thing, you just don't give it away for nothing".
The day after the presidential election, according to the affidavit, Mr Blagojevich was recorded as saying: "I've got this thing and it's [expletive] golden, and uh, uh, I'm just not giving it up for [expletive] nothing."
Mr Obama said on Thursday he had not discussed his vacant Senate seat with Mr Blagojevich and was confident that nobody on his staff had either.
He promised to release shortly a record of any contacts with the governor's office regarding the vacancy.
"Let me say that this Senate seat does not belong to any politician to trade - it belongs to the people of Illinois and they deserve the best possible representation," he told reporters in Chicago.
Mr Obama's Chief of Staff Rahm Emanuel, who, like the president-elect and Mr Blagojevich, has his political roots in Illinois, is not a target of the FBI's investigation, officials said.
Mr Blagojevich caused outrage by returning to work on Wednesday, a day after he was released on bail having appeared before a federal judge.
His lawyer told reporters that Mr Blagojevich believed he had done nothing wrong and had no plans to resign.