Federal prosecutors on Tuesday unsealed conspiracy, assault and other charges against 15 people accused of violently impeding immigration enforcement officers in Minneapolis during an immigration crackdown earlier this year.

Daniel N. Rosen, the top federal prosecutor in Minnesota, said the defendants were members of two Minneapolis-based Antifa groups, a far-left movement. Twelve of the defendants were arrested on Tuesday, Mr. Rosen said, one was already in custody for other charges, and two remained at large. Antifa, named for its antifascist political alignment, is not an organization with a leader but a diffuse protest culture of activists who want to stop the far right.

The defendants were charged with conspiracy to impede or injure a federal officer; solicitation to commit a crime of violence; interstate stalking; assault on a federal officer; and destruction of government property.

“Today’s charges and arrests reflect a broad federal effort to address organized lawless behavior, which seeks to disrupt the execution of federal law, endanger law enforcement, and importantly endanger the very communities that these defendants falsely claim to be protecting,” Mr. Rosen said during a news briefing on Tuesday.

It was unclear whether the defendants had legal representation and whether they had entered pleas.

The 94-page conspiracy indictment was filed at a particularly fraught moment for Minnesota federal prosecutors, who have had trouble sustaining many criminal cases they have filed against Immigration and Customs Enforcement protesters since the Trump administration’s crackdown in the state began late last year. Defense lawyers say that about half of the 36 cases charging individual defendants with assaulting or interfering with federal agents assigned to the crackdown have been dismissed. Judges have questioned the evidence underlying the accusations.

At the news conference on Tuesday, reporters confronted Mr. Rosen with the struggles that his office has faced in prosecuting officer assault cases, and he sought to defend the new indictment. “You watch how this case plays out, you watch how the evidence plays out,” he said.

The Trump administration, through executive actions, has prioritized bringing criminal cases against anyone associated with antifa, especially those who have protested his aggressive immigration crackdown. Democrats have said that the administration was attempting to silence dissent.

This is a developing story. Check back for updates.