A hostage-taker who detained four people at a synagogue in a suburb of Dallas, Texas, was a British citizen, reports say.
The man interrupted a morning service in Colleyville on Saturday and has since died.
Police deployed special weapons teams, while FBI negotiators spent hours talking to the assailant.
Explosions and gunfire could be heard before the 10-hour stand-off ended. The hostages have been freed unharmed.
In a statement, the UK Foreign Office said it was aware of the death of a British man in Texas and was in contact with the local authorities. It is not yet clear how the hostage-taker died or who he was.
The four people taken hostage included the synagogue’s rabbi, according to US media reports.
The service was being streamed online when the incident began. One of the hostages was released unharmed six hours later, with the other three being led to safety by police several hours after that.
President Joe Biden was briefed about the developing situation.
The incident began at around 11:00 local time (16:00 GMT) when police were called to the Congregation Beth Israel synagogue. People were evacuated from the area shortly after.
A live stream of the Shabbat morning service on Facebook captured audio of a man talking loudly. He could be heard saying: “You get my sister on the phone” and “I am gonna die.”
He was also heard saying: “There’s something wrong with America.” The feed has since been taken down.
The hostage-taker was heard demanding the release of Aafia Siddiqui, a Pakistani neuroscientist who is currently serving an 86-year prison term in the US, law enforcement officials told local media.
Siddiqui was convicted of trying to kill US military officers while in custody in Afghanistan. Thousands took to the streets in Pakistan to protest against her conviction in 2010.
After the Islamic State (IS) group kidnapped American journalist James Foley in Syria in 2012, they emailed his family demanding the release of Siddiqui.
A lawyer representing Siddiqui told CNN in a statement that the hostage-taker was not her brother, saying Siddiqui’s family condemned his “heinous” actions.
Texas resident Victoria Francis, who was watching the live stream before it cut out, told the Associated Press that she heard the man rant against America and claim he had a bomb.
“He was pretty irritated and the more irritated he got, he’d make more threats,” she said.