Two people have been killed and multiple individuals wounded in a shooting at a federal Immigration and Customs Enforcement (Ice) field office in Dallas.
The shooter has also been killed after suffering a self-inflicted gunshot wound, federal officers said.
Homeland Security Secretary Kristi Noem confirmed there were "multiple fatalities" in the shooting.
"The obsessive attack on law enforcement, particularly ICE, must stop. I'm praying for everyone hurt in this attack and for their families," US Vice President JD Vance wrote on X.
Ms Noem wrote on X: "There was a shooting this morning at the Dallas ICE Detention Facility.
"Details are still emerging, but we can confirm there were multiple injuries and fatalities. The shooter is deceased by a self-inflicted gunshot wound."
High-ranking Dallas Police Department officials say no law enforcement officers were injured, but that three people were shot and two were killed.
Ms Noem added: "While we don't know the motive yet, we know that our ICE law enforcement is facing unprecedented violence against them. It must stop. Please pray for the victims and their families."
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Dozens of police personnel are at the scene
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A police officer on the phone at the scene
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Authorities said the shooter opened fire when the facility was open during the transfer of detainees.
He attempted to force his way into the detention facility.
Department of Homeland Security spokeswoman Tricia McLaughing told Fox News that it was "just a month ago to the day that there was a viable bomb threat" in Dallas.
She said: "This location, it looks like it's been targeted, and we don't know how long this individual has been planning this act.
Emergency services closed off roads around where the shooting happened
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"It looks like he could have been watching to look at the processing and see what happens on a day-to-day basis at this Dallas field office.
"But [these are] all answers that Homeland Security investigation is going to get down to the bottom of."
Senator Ted Cruz confirmed he is aware of the shooting and noted that his team are monitoring the situation.
Mr Cruz said: "My team and I are closely monitoring the situation at the ICE Detention Facility in Dallas.
The shooting has caused travel chaos in the area
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"We are praying for the swift recovery of those injured, and we are deeply grateful to the brave first responders who rushed to the scene."
The shooter was found dead on the roof of a nearby building, local ABC affiliate WFAA reported, citing sources.
"Preliminary information is a possible sniper," ICE acting Director Todd Lyons told CNN.
Police were expected to hold a news briefing later in the morning.