(CNN) -- Illinois Gov. Pat Quinn called Friday for Sen. Roland Burris to resign.
Sen. Roland Burris of Illinois is facing pressure to step down, even from fellow Democrats.
"At this time we have a senator who has a cloud over his head," Quinn said at a news conference. "It's time (for Burris) to put the interest of the people of the land of Lincoln ahead of his own and step aside and resign from office.
"I think very highly of his career. He's done so many good things," Quinn said.
"But at this time... to step away and resign [would be] a heroic act."
It was a "gigantic mistake" for Burris to accept a Senate appointment from disgraced former Gov. Rod Blagojevich, Quinn said. Quinn replaced Blagojevich when he was removed from office last month.
Burris has "no plans to resign" and intends to "let the process work itself out in Illinois and in the Senate Ethics Committee," an aide to Burris told CNN. The senator is not planning to officially respond to Quinn, the aide said. Watch Quinn say why his "good friend" should resign »
As pressure against Burris mounted Friday, the Illinois Democrat's top aide stepped down and returned to his position with Senate Majority Leader Harry Reid.
Darrel Thompson said he was "temporarily detailed" to Burris and did not elaborate on why he was returning to Reid's office.
But a Democratic leadership aide, who asked not to be named given the sensitivity of the matter, said Thompson was left with no choice but to resign.
"In light of the conflicting statements, he felt it was something he could no longer help out with," the source said.
The Ethics Committee has launched an investigation of Burris in the wake of disclosures that he spoke with Blagojevich's brother about possibly raising money for the former governor. Watch troubles mount for Burris »
The Sangamon County, Illinois, state's attorney is also considering whether to file perjury charges against Burris.
Burris insisted Wednesday that he was innocent of any wrongdoing in his appointment to the Senate seat formerly held by President Obama.
Burris told reporters earlier in the week that he informed Blagojevich's brother Robert in November that no one was willing to give money to the governor and that it would be inappropriate to raise money because he was interested in being appointed to the Senate.
During his testimony under oath in Blagojevich's impeachment trial, however, Burris failed to mention any such conversations when asked about contacts with the governor's office. He later acknowledged that his testimony might be incomplete and filed an affidavit correcting it.
Looking ahead to a possible Burris resignation, Quinn said he supported a bill introduced in the Illinois Legislature that would set up a special election for all future U.S. Senate vacancies.
"It is time to squarely address the issue and do what's right for the public interest," Quinn said. iReport.com: Should Burris resign?
Illinois needs a "clear process for dealing with the issue of vacancies when it comes to the United States Senate," Quinn said.
The bill would allow the governor to set the date of a special Senate primary within 72 days of the vacancy. A general election would follow within six weeks after the primary.
The governor would be empowered to name a temporary replacement until the special election.
Quinn said that if given the power to name a replacement he would not name someone with an interest in running in the special election.
Quinn was sworn in as Illinois' governor on January 29. He had been serving as the state's lieutenant governor until Blagojevich was removed from office.
CNN Senior Congressional Correspondent Dana Bash contributed to this report.