U.S. president-elect Barack Obama came out against Illinois Gov. Rod Blagojevich's decision on Tuesday to name his Senate replacement, saying he agreed the legislative body "cannot accept" the scandal-tarred governor's selection.

Earlier in the day, a defiant Blagojovich exercised his prerogative as governor and named 71-year-old former state attorney general Roland Burris to fill Obama's vacated seat.

Blagojevich was arrested earlier this month on charges that he tried to sell or trade the seat to the highest bidder. He denies all wrongdoing.

In a statement released Tuesday evening, Obama called Blagojevich's move "extremely disappointing."

"Roland Burris is a good man and a fine public servant, but the Senate Democrats made it clear weeks ago that they cannot accept an appointment made by a governor who is accused of selling this very Senate seat," Obama said.

"I believe the best resolution would be for the governor to resign his office and allow a lawful and appropriate process of succession to take place."

In Washington Tuesday, Senate Democrats reiterated that no one appointed by Blagojevich would have the credibility to serve.

In a letter, the senators said that Blagojevich should not make the appointment because it is unfair to Burris, unfair to the people of Illinois and ultimately won't stand.

The U.S. Constitution and Senate rules of procedure give senators the right to rule on whether a nominee for a seat is qualified, but legal experts say court challenges are likely if Burris is rejected.

Flanked by Burris at the podium in Springfield, Ill., Tuesday afternoon, Blagojovich said he had no choice but to appoint a new senator to fill Obama's seat, which was vacated when he won last month's presidential election.

Nominee's integrity 'unquestioned'

Burris, he said, "is a man of unquestioned integrity [and] extensive experience and is a wise and experienced senior statesman of Illinois. Don't allow the allegations against me to taint this good and honest man."

Burris said he was proud to accept the nomination and said he had no comment on the governor's legal problems.

"I'm accepting an appointment by the governor to the United States Senate, that's it," he said.

On Dec. 9, the Illinois governor was arrested by FBI agents and charged with conspiracy to commit fraud as well as solicitation of bribery.

An FBI affidavit says Blagojevich was intercepted on wiretaps conspiring to sell or trade the seat vacated by Obama when he won the U.S. presidential election last month.

In an effort to limit political damage to the incoming Obama administration, members of his own party have led calls for Blagojevich's resignation.

Obama once supported governor

Obama has publicly distanced himself from the governor, but he supported him during his first campaign for the governorship and his top aide, David Axelrod, was also a close political adviser to Blagojevich in recent years.

The 52-year-old governor has been the subject of several other high-profile investigations into alleged corruption and is described in local media in Illinois as one of the least popular governors in state history.

His administration has had to cope with a series of scandals and often has trouble getting legislation passed, despite a Democratic majority in the state assembly.

With files from the Associated Press