CHICAGO (Reuters) - U.S. Representative Jesse Jackson Jr. began a medical leave of absence from Congress on June 10 and is being treated for exhaustion, his office said on Monday.

The offices of the Chicago Democrat, who has served in Congress since 1995, remain open to serve constituents, said a statement from Jackson spokesman Frank Watkins.

"He asks that you respect his family's privacy," the statement said.

U.S. Representative Danny Davis, a fellow Chicago Democrat, said he was surprised to learn of the leave because Jackson was "his normal, jovial self" two weeks ago.

Jackson, who this spring won a competitive primary contest, is under investigation by the House Ethics Committee for his alleged involvement in the scheme by imprisoned former Illinois Governor Rod Blagojevich to sell President Barack Obama's former U.S. Senate seat. Jackson testified at Blagojevich's trial that he sought the Senate seat but denied knowing about any offers of money by his supporters to the then-governor to appoint Jackson.

Jackson's father is civil rights leader Reverend Jesse Jackson.

(Reporting By Andrew Stern; Writing by Corrie MacLaggan; Editing by Eric Walsh)