WASHINGTON - US House Speaker Paul Ryan's abrupt announcement that he will retire rather than seek another term in Congress as the steady if reluctant wingman for President Donald Trump sent new ripples of uncertainty through a Washington already on edge and a Republican Party bracing for a rough election year.

Ryan said he had decided to end his 20-year career because he doesn't want his children growing up with a "weekend dad", but it will create a vacuum at both ends of Pennsylvania Avenue.

It will leave congressional Republicans without a measured voice to talk Trump away from what some see as damaging impulses, and it will rob Trump of an influential steward to shepherd his more ambitious ideas into legislation.

Trump praised Ryan as "a truly good man".

It's unusual for a House speaker, third in line to succeed the president, to turn himself into a lame duck, especially so for Ryan, a once-rising GOP star who is only 48 and was the party's vice-presidential candidate in 2012. His decision fueled fresh doubts about the party's ability to fend off a Democratic wave, fed by opposition to Trump, in November. And it threw the House into a leadership battle that could end up pushing Ryan aside sooner than he intended and crush any hopes for significant legislation before the election.

Speculation over Ryan's future had been swirling for months, but as he dialed up colleagues and spoke by phone with Trump, the news stunned even top allies.

Ryan announced his plans at a closed-door meeting of House Republicans. Representative Mark Walker of North Carolina said an emotional Ryan "choked up a few times trying to get through" his remarks and received three standing ovations.

He later briefly thanked Trump in public for giving him the chance to move GOP ideas ahead.

While Ryan was crucial in getting the tax cuts passed, a prime Trump goal, he and the president have had a difficult relationship. Trump showed impatience with Congress' pace in dealing with his proposals, and Ryan had to deal with a president who shared little of his interest in policy detail.

Still, for many Republicans, it's unclear who will be left in leadership to counterbalance Trump. Ryan has been "a steady force in contrast to the president's more mercurial tone," said Representative Mark Sanford of South Carolina. "That's needed."

The speaker had been heading toward this decision since late last year, said a person familiar with his thinking, but as recently as February he had considered running for another term. His own father died suddenly of a heart attack when he was 16, and though Ryan is in good health, the distance from his family weighed on him. A final decision was made over the two-week congressional recess, which he partly spent on a family vacation in the Czech Republic.

Ap - Xinhua