Illinois Gov. Rod Blagojevich named former state Attorney General Roland Burris to fill President-elect Barack Obama's vacant U.S. Senate seat on Tuesday, stunning lawmakers both in his home state and in Washington, where Senate Democrats vowed to block the appointment.

Illinois Secretary of State Jesse White, who must certify the appointment, said he will not do so and Senate leaders reiterated that they would not accept anyone appointed by Blagojevich.

Blagojevich, claiming he was obligated by law to fill the vacant Senate seat, called Burris -- a lobbyist and campaign donor to the governor -- a candidate of "unquestioned integrity" and urged the public not to "allow the allegations against me to taint this good and honest man."

"It is truly regrettable that despite requests from all 50 Democratic Senators and public officials throughout Illinois, Gov. Blagojevich would take the imprudent step of appointing someone to the United States Senate who would serve under a shadow and be plagued by questions of impropriety," Senate Democrats said in a written statement.

Obama sided with the Senate leadership, saying in a written statement that the governor's decision was "disappointing" and that he should resign so a "lawful and appropriate process of succession" can take place.

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"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. I agree with their decision," the president-elect said.

Illinois Lt. Gov. Pat Quinn, who is next in line to be governor, told reporters that the Burris appointment was an "insult to the people of Illinois" and urged the public to "stand firm" against the governor's actions.

"Rod Blagojevich has unclean hands, and he should not be able to make an appointment to any office whatsoever," Quinn said.

Blagojevich is facing federal corruption charges and impeachment proceedings after being accused of trying to sell Obama's seat.

Despite the cloud of allegations surrounding him, Blagojevich said he was confident his selection of Burris would be upheld.

"The people of Illinois are entitled to have two United States senators representing them in Washington, D.C. As governor, I am required to make this appointment," Blagojevich said. "This is about Roland Burris as the United States senator -- not about the governor who makes the appointment."

Burris said he has no involvement in the charges against the governor and asked voters to place the "same faith and trust in me as they have in the past."

U.S. Rep. Bobby Rush also stepped to the podium and endorsed Burris, who is black, as a "worthy" and "esteemed" candidate. Rush had been urging Blagojevich to select an African-American to replace Obama, who had been the only black in the Senate.

Concerns are widespread that any appointment by Blagojevich will be tainted since the governor is facing charges for his alleged attempts to extract favors and contributions from potential candidates. Several unidentified Senate candidates are referenced in transcripts of wiretapped conversations with Blagojevich; Burris has not been identified as one of them.

Blagojevich's lawyer, Ed Genson, told reporters just two weeks ago that because of the threats from Senate lawmakers, the governor would not attempt to appoint anybody to the seat.

Illinois House Republican Leader Tom Cross told FOXNews.com he was shocked by the governor's turnaround.

"It's unbelievable," he said. "I can't comprehend that it's even happening."

But he predicted that Burris and Blagojevich would fight hard to defend the legitimacy of the decision.

"It's complete disregard for the will of the people of our state," said Illinois state Rep. Susana Mendoza, a Democrat, calling the move "brazen" and "disgusting."

The Chicago Tribune reported that Burris, 71, has been interested in the appointment since Obama's Election Day victory, though he was not considered a top candidate for the job. He reportedly stepped up his lobbying effort after the governor's arrest.

Burris is a prolific contributor to Democratic candidates, including Blagojevich. State campaign finance records show he and his wife have donated $4,500 to Blagojevich's campaign fund since 2004. Burris has also contributed to Obama and Vice President-elect Joe Biden.

Burris served as state attorney general from 1991 to 1995. He earlier served as state comptroller, and made history as the first black elected to statewide office.

Blagojevich's announcement could complicate matters for the Illinois House panel examining grounds for his impeachment. If Burris is accepted, the scenario could implicitly affirm the governor's authority.

Genson has argued that the threshold for impeachment has not been met.

Click to read the statement on Blagojevich from U.S. Senate Democrats

Click to read Burris' resume

Click to read more in the Wall Street Journal