WASHINGTON (REUTERS) - US prosecutors filed criminal charges of fraud and conspiracy on Friday against former Chicago Representative Jesse Jackson Jr, accusing him and an unnamed co-conspirator of misusing US$750,000 (S$927,600) in campaign funds.

Jackson, 47, released a statement as the charges were filed, admitting mistakes but did not immediately enter a plea.

"I offer no excuses for my conduct, and I fully accept my responsibility for the improper decisions and mistakes I have made," said Jackson, a Democrat.

Once considered one of the most promising black politicians in the United States, Jackson resigned his congressional seat on Nov 21 for health reasons, acknowledging at the time that he was under investigation by the Federal Bureau of Investigation.

Prosecutors said at least seven people were involved in the scheme to divert campaign funds to personal uses, identified in court papers with names such as "Co-Conspirator 1".

"The goal of the conspiracy was for defendant Jesse Jackson Jr and Co-Conspirator 1 to enrich themselves by engaging in a conspiracy and a scheme to defraud in which they used funds donated to the Campaign for their own personal benefit," the court documents said.

Prosecutors filed a related charge against Jackson's wife, Sandi Jackson, accusing her of knowingly filing false tax returns. Sandi Jackson resigned her seat as a Chicago city councilwoman last month.

Among the accusations is that Jackson shipped a US$43,350 men's Rolex watch purchased with campaign funds to his D.C. address. He also shipped fur capes and parkas purchased with US$5,150 in campaign funds to the Beverly Hills home of an unnamed person, the documents said.

Under federal sentencing guidelines, if convicted, Jackson faces a maximum penalty of five years in prison and his wife three years, but defendants often are sentenced to much less than the maximum term.

Jackson disappeared from public view early in the summer of last year, and speculation swirled for weeks about his condition. He said in late June he had taken a leave of absence two weeks earlier for treatment of what was then described as exhaustion.

Jackson issued a statement on July 5 that said his health problems were more serious and he needed extended in-patient treatment for unspecified "physical and emotional ailments".

On July 11, his physician said the congressman was receiving intensive care for a "mood disorder" and was expected to make a full recovery. The Mayo Clinic announced on July 27 that Jackson had been admitted.

Jackson was treated for at least six weeks at Mayo for bipolar disorder, sometimes called manic depression. It is marked by highs and lows of mood, and can be treated by medication and psychological counseling.

In addition to the federal investigation of his campaign finances, Jackson had been the subject of a House ethics committee probe over an alleged bribe offered by a Jackson supporter in 2008 to then-Illinois Governor Rod Blagojevich.

The bribe was said to be intended to entice Blagojevich to appoint Jackson to the US Senate seat vacated by President Barack Obama.

Jackson has admitted to lobbying for the seat, but denied knowing about any money offered to Blagojevich, who has since been convicted of corruption and imprisoned.

Jackson had served in Congress since 1995 and was easily re-elected in November last year, despite his absence from the district. His resignation came two weeks after the election.