US House Speaker Ryan will not seek re-election: aide

The top Republican in the US House of Representatives, Paul Ryan, has decided to retire when his term ends, casting his party into a leadership fight ahead of crucial mid-term elections.

The bombshell was delivered by the speaker's counselor, Brendan Buck, who said Ryan would not seek re-election in November.

"This morning Speaker Ryan shared with his colleagues that this will be his last year as a member of the House.

"He will serve out his full term, run through the tape, and then retire in January," Buck said in a statement.

Ryan, who reluctantly assumed the House leadership in 2015 and never fully embraced President Donald Trump, has given no sign of his future political ambitions.

Trump paid tribute to Ryan as "a truly good man." "While he will not be seeking re-election, he will leave a legacy of achievement that nobody can question. We are with you Paul!" the president tweeted following the announcement.

Buck said the 38-year-old congressman from Wisconsin was looking forward to spending more time with his young family.

"After nearly twenty years in the House, the speaker is proud of all that has been accomplished and is ready to devote more of his time to being a husband and a father," Buck said.

"While he did not seek the position, he told his colleagues that serving as speaker has been the professional honor of his life, and he thanked them for the trust they placed in him." Chuck Schumer, the top Democrat in the US Senate, praised Ryan as "a good man who is always true to his word."