Story highlights Rep. Jesse Jackson is undergoing an "extensive inpatient evaluation"

The Mayo Clinic in Minnesota is one of the nation's top hospitals

Jackson hasn't been on Capitol Hill since last May

Earlier this month, his office said he was getting treatment "for a mood disorder"

Rep. Jesse Jackson Jr. is at the Mayo Clinic undergoing an "extensive inpatient evaluation for depression and gastrointestinal issues," the congressman said in a statement released Friday via the hospital.

The Illinois Democrat and son of the Rev. Jesse Jackson, the civil rights leader, has not been on Capitol Hill since late May. Earlier in July -- one month after announcing he was on a leave of absence due to a "medical condition" -- the congressman's office released a statement saying he was "receiving intensive medical treatment at a residential treatment facility for a mood disorder."

The name of the facility was not announced at the time. But Friday's statement makes clear that Jackson is, at least now, being treated at the Mayo Clinic in Rochester, Minnesota, one of the nation's and world's most renowned hospitals.

"Further information will be released as Congressman Jackson's evaluation proceeds," said the statement from Jackson, which was distributed by the Mayo Clinic. "Congressman Jackson and his family are grateful for the outpouring of support and prayers that have been received throughout his care."

In its announcement earlier this month, Jackson's office quoted an unnamed doctor as saying the congressman was "responding positively to treatment and is expected to make a full recovery.".

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Jackson's illness comes as the House Ethics Committee is examining allegations that in 2008 he or or one of his associates offered to raise funds for then-Illinois Gov. Rod Blagojevich in exchange for Jackson being appointed to the Senate seat vacated by Barack Obama after he was elected president.

The congressman has maintained his innocence and pledged to continue to cooperate with authorities.

Blagojevich was convicted last year on corruption charges in connection with his efforts to profit from appointing the successor to the Senate seat. He began serving a 14-year sentence in March.

In a separate incident, Jackson apologized to his constituents in September 2010 after the Chicago Sun-Times reported a Chicago businessman told federal investigators that Jackson had asked him to pay for a restaurant hostess to fly between Washington and Chicago several times.

He said he was "deeply sorry" that he had disappointed some supporters."

House Minority Leader Nancy Pelosi, D-California, said earlier this month that Jackson should disclose information about his health struggles on his own timetable. But Steny Hoyer of Maryland, the House minority whip, said more information should be provided.

Another Democratic congressman, Emanuel Cleaver, said he'd spoken with members of Jackson's family and believed the Illinois legislator is "fine (and) he'll be back."

Cleaver, the chairman of the Congressional Black Caucus, said he found it "frustrating and disappointing" that some other Democrats on Capitol Hill had called on Jackson to disclose more about his health struggles.

"This is not about a congressman. This is about a human being who is sick," Cleaver said. "This is not a political matter, it's a health matter."