UPDATE | US Rep. Paul Ryan won't run for re-election

WASHINGTON (AP) — Republican House Speaker Paul Ryan will not run for re-election, his office announced today, injecting another layer of uncertainty as Republicans face worries over losing their majority in the fall.

Ryan's plans have been the source of much speculation and will set off a scramble among his lieutenants to take the helm. A self-styled budget guru, Ryan had made tax cuts a centerpiece of his legislative agenda, and a personal cause, and Congress delivered on that late last year.

Ryan, 48, announced his plans at a closed-door meeting of House Republicans this morning, according to those present. His tone was somber, and he read directly from prepared remarks.

"After nearly 20 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," Ryan adviser Brendan Buck said in a statement. "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."

Ryan will serve out his term and retire in January, Buck said.

Ryan, a Republican from Janesville, Wis., was first elected to Congress in 1998. Along with Reps. Eric Cantor and Kevin McCarthy, he branded himself a rising "Young Gun" in an aging party.

He became the GOP presidential nominee Mitt Romney's running mate in 2012.

Ryan was pulled into the leadership job by the abrupt retirement of House Speaker John Boehner of Ohio in 2015. Boehner had struggled to wrangle the chamber's restless conservative wing and failed to the seal big-picture deals on fiscal policy he sought. Ryan had more trust with the hardliners in the House, but had no more success in brokering fundamental reform of entitlement he sought.

He ultimately had to wrestle with another unexpected challenge: President Donald Trump, a president with little of Ryan's interest in policy detail or ideological purity. The two have had not had a close working relationship.

9:26 a.m.

WASHINGTON (AP) — Republican House Speaker Paul Ryan will not run for re-election, people close to the Wisconsin lawmaker said today.

Ryan's plans have been the source of much speculation amid Republican concerns over keeping their majority in the House of Representatives. Ryan had made tax cuts a centerpiece of his legislative agenda, and Congress delivered on that late last year.

Ryan, 48, planned to face reporters later this morning.

Two people with knowledge of Ryan's thinking said he has decided against seeking another term, but they did not say why. Both sought anonymity because they were not authorized to speak publicly.

Ryan, a Republican from Janesville, Wis., was first elected to Congress in 1998 and became speaker in 2015 after former House Speaker John Boehner of Ohio retired. He was former GOP presidential nominee Mitt Romney's running mate in 2012.

Ryan and his wife have three children.