A sniper opened fire on the Dallas Immigration and Customs Enforcement field office on Wednesday morning, killing one detainee and critically wounding two other detainees, the Department of Homeland Security said.

The suspected shooter at a Dallas ICE facility has been identified by law enforcement officials as 29-year-old Joshua Jahn, multiple law enforcement sources tell ABC News.

DHS previously said two detainees were killed and one was injured; the agency later issued a correction saying one died and two were shot but survived.

One of the wounded is a Mexican national, according to Mexico's Ministry of Foreign Affairs.

Although only detainees were shot, the Department of Homeland Security called the shooting "an attack on ICE law enforcement."

The shooter, who was on a nearby rooftop, "fired indiscriminately at the ICE building, including at a van in the sallyport where the victims were shot," DHS said in a statement.

The shooter died from a self-inflicted gunshot wound, officials said.

Vice President JD Vance said during remarks in North Carolina on Wednesday that evidence that has not yet been released shows the shooter was a "left-wing extremist" who was "politically motivated to go after people who are enforcing our border."

The FBI said the shooting is being investigated "as an act of targeted violence."

FBI special agent Joe Rothrock said it appeared that rounds "found near the suspected shooter contain messages that are anti-ICE in nature."

FBI Director Kash Patel released images of recovered unspent shell casings, including one engraved with the phrase "ANTI-ICE," and DHS released a photo that appears to show a gunshot in an American flag display.

Mayra, a migrant who left Nicaragua four years ago, told ABC News she was with her husband at the ICE facility waiting for her immigration status check-in appointment when they heard gunshots outside.

She said security officers inside screamed at them to get down and the building immediately went on lockdown.

Mayra said her daughter, who was outside the facility at the time in case she got detained, screamed and ran for cover.

Mayra said she plans to return to the facility on Thursday for her new appointment.

The shooting comes as ICE has been ramping up deportation efforts throughout the country and DHS says ICE officers are facing a more than a 1,000% increase in assaults against them.Two Texas facilities were targeted this July: a police officer was shot at an ICE detention facility in Alvarado and a gunman opened fire at the entrance of the Border Patrol sector annex in McAllen.

In the wake of Wednesday's shooting, federal officials are stressing that attacks on ICE and law enforcement must end.

"Our prayers are with the families of those killed and our ICE law enforcement. This vile attack was motivated by hatred for ICE," DHS Secretary Kristi Noem said in a statement. "For months, we’ve been warning politicians and the media to tone down their rhetoric about ICE law enforcement before someone was killed. This shooting must serve as a wake-up call."

"This is the second time I've had to stand in front of you and talk about a shooter at one of my facilities. And I think that the takeaway from all of this is that the rhetoric has to stop," Dallas ICE official Joshua Johnson said at the news conference.

"This needs to stop," Sen. Ted Cruz, R-Texas, said at a news conference. "Violence is wrong, politically motivated violence is wrong."

Vance said, "We're praying both for our ICE agents, but also for everybody who's affected by this terrible attack."

House Democratic leaders in a statement thanked the first responders and offered their condolences to the victims' families.

"No one in America should be violently targeted, including our men and women in law enforcement who protect and serve our neighborhoods, and the immigrants who are too often the victims of dehumanizing rhetoric," the Democrats' statement continued. "The political and ideologically-motivated violence in America has reached a breaking point this year. We need leaders who bring the country together in moments of crisis."

Acting ICE Director Todd Lyons said he would put all ICE facilities on a higher alert to protect agents and civilians carrying out the agency’s mission.