Image caption Senator Lieberman is stepping down after 40 years in elected office

Former US vice presidential candidate Senator Joe Lieberman has announced he is retiring next year.

The politician, who has represented Connecticut as a Democrat and an independent, made the announcement at a news conference.

The 68-year-old has served 24 years in the US Senate and 40 years in elected office.

He has a reputation for being strong-minded and reaching across party lines.

"The reason I have decided not to run for re-election in 2012 is best expressed in the wise words from Ecclesiastes: 'To everything there is a season, and a time to every purpose under Heaven,'" Mr Lieberman told reporters.

"For me, it is time for another season and another purpose under Heaven," he added.

Mr Lieberman, who ran alongside Al Gore in the 2000 presidential election, tried and failed to run for president in 2004.

In 2006 he ran as an independent, rather than a Democrat, in the Senate primary in Connecticut.

Two years later he upset many Democrats by backing Republican John McCain for the presidency.