WASHINGTON — The House committee investigating the Jan. 6 attack on the Capitol issued two subpoenas on Wednesday for the leaders of a white nationalist movement that helped bring a crowd to Washington ahead of the riot.

The committee issued subpoenas to Nicholas J. Fuentes and Patrick Casey, whom the panel described as leaders of the “America First” or “Groyper” movement and who were on the Capitol grounds last Jan. 6. Mr. Fuentes, a white nationalist, online provocateur and activist, has allied with Representative Paul Gosar, a far-right Republican from Arizona who helped lead objections in Congress to the certification of President Biden’s victory.

The subpoenas demonstrated the committee’s intensifying focus on the rallies that led up to the mob violence and how those with extremist views were drawn to former President Donald J. Trump’s false claims of widespread voter fraud.

The panel instructed the men to turn over documents related to their activities and submit to interviews in February.

“The Select Committee is seeking facts about the planning, coordination, and funding of events that preceded the violent attack on our democracy,” said Representative Bennie Thompson, Democrat of Mississippi and chairman of the committee. “We believe the individuals we have subpoenaed today have information relevant to those questions, and we expect them to cooperate with the committee.”

The committee said the two men participated in a series of events leading up to last Jan. 6, in which they promoted false claims about the election, including at two rallies in Washington, where they called for the destruction of the Republican Party for failing to overturn the election.

According to reports cited by the committee, both Mr. Fuentes and Mr. Casey received tens of thousands of dollars in Bitcoin from a French computer programmer. The F.B.I. has scrutinized that money to assess whether any of it was linked to the Capitol attack or otherwise used to fund illegal activity, the panel said.

Mr. Fuentes marched at both the Unite the Right rally in Charlottesville, Va., in 2017 and outside the Capitol on Jan. 6, 2021. He has promoted a message that the nation is losing “its white demographic core.” Other conservative organizations have denounced him as a Holocaust denier and a racist.

Even so, Mr. Fuentes has found an ally in Mr. Gosar, who was censured in November after posting an animated video that depicted him killing a Democratic congresswoman and assaulting Mr. Biden.

Mr. Gosar was the keynote speaker at a conference hosted by Mr. Fuentes’s group last year, the only member of Congress to participate. Mr. Gosar has spread America First’s motto and projects on Twitter and written to the F.B.I. on congressional letterhead in Mr. Fuentes’s defense. In return, Mr. Fuentes has praised Mr. Gosar on his show and social media channels and urged his followers to donate money to his campaign.

At least one of Mr. Fuentes’s followers, Christian Secor, a California college student, has been charged with breaking into the Capitol on Jan. 6. Mr. Secor, who breached the Senate floor carrying an America First flag, posted a photo of himself posing with Mr. Fuentes on Twitter before the attack with a caption reading, “Kinda epic doe?”

As the Capitol attack began, Mr. Casey wrote on Telegram at 2:30 p.m., “It’s happening.”

A day after the attack, Mr. Fuentes wrote on Twitter that the assault on the Capitol was “awesome and I’m not going to pretend it wasn’t.”

In June of that year, Mr. Fuentes again endorsed the mayhem of Jan. 6, adding: “And Trump was awesome because he was racist. Trump was awesome because he was sexist.”

Mr. Fuentes also is an associate of Ali Alexander, the prominent “Stop the Steal” organizer who has praised him, despite his racist views, for his ability to draw a crowd. Mr. Alexander is cooperating with the Jan. 6 committee and has turned over voluminous documents.

The panel said Mr. Casey reportedly broke ties with Mr. Fuentes after the Jan. 6 attack.

On Telegram, Mr. Fuentes complained Wednesday the committee didn’t announce his subpoena separately. “They couldn’t give me my own post? What a rip,” he wrote.

The two men could not be reached immediately for comment.

Catie Edmondson contributed reporting.