Sen. Roland Burris' chief of staff is stepping down as pressure on the Democratic lawmaker to resign intensifies.

Interim Chief of Staff Darrel Thompson is going back to work as a senior adviser to Senate Majority Leader Harry Reid

Thompson said in a Friday statement he was temporarily detailed three weeks ago to serve as Burris' chief of staff and the role ended Friday.

It was not immediately clear who would replace Thompson.

Burris is under pressure to resign from the Senate for not disclosing contacts with advisers to former Gov. Rod Blagojevich, who appointed Burris to the seat before being impeached and ousted last month over corruption allegations.

Earlier Friday, Illinois Gov. Pat Quinn called on Burris to resign, joining a growing chorus of politicians and newspapers. 

The Democratic governor said it was a "mistake" for Burris to accept the Senate appointment. 

"I would ask my good friend Senator Roland Burris to put the interest of the people of the land of Lincoln ahead of his own and step aside," Quinn said at a news conference Friday.

Quinn called Burris an honorable man but said there's a shadow over his service in the Senate.

Quinn said a new senator should be chosen by special election to fill the seat once held by Barack Obama.

Burris initially said there was no discussion of him doing any favors in exchange for the appointment. But Burris later acknowledged he did discuss the vacant seat with Blagojevich's friends and allies. He claims he was asked to raise money for Blagojevich but couldn't find anyone willing to contribute.

White House press secretary Robert Gibbs would not go so far as to call on Burris to resign Friday but did urge him to take time over the weekend to think about his future.

Burris needs to "come up with an explanation that satisfies" questions about the conflicting statements he has made, Gibbs said, adding that Obama supports "an investigation that would get some full story out."

Burris has stopped speaking publicly and answering any more questions about the evolving story of his Senate appointment.

The Associated Press contributed to this report.