Democratic congressman Jared Golden has announced his retirement, saying he will not be running for re-election in his battleground Maine district.

The 43-year-old cited political violence and extreme polarisation in the US as reasons why he is leaving office, penning an opinion piece published in his hometown newspaper.

"After 11 years as a legislator, I have grown tired of the increasing incivility and plain nastiness that are now common from some elements of our American community," the congressman wrote.

Golden's district elected Trump in the 2024 election by nine points, and his seat has been identified as vulnerable for Democrats going into the midterm elections next year.

The announcement comes amid a bitter redistricting war across the US, with both conservative and democratic-led states changing voting lines to shore up their party's chances of controlling the US House of Representatives.