An FBI Hostage Rescue Team stormed a synagogue in Colleyville, Texas, on Saturday night to free three remaining hostages of a gunman who had disrupted a religious service and began a standoff with police more than 10 hours earlier.

President Joe Biden described the hostage-taking as an “act of terror”.

All the hostages were safely released on Saturday night and the gunman was dead, Colleyville police chief Michael Miller told a news conference. The FBI identified the man killed after taking hostages as 44-year-old British national Malik Faisal Akram. The FBI declined to confirm the cause of his death, saying it was still under investigation.

The gunman had initially taken four people hostage, including the rabbi, at the Congregation Beth Israel, officials said. One hostage was released unharmed six hours later.

Reporters said they heard the sound of explosions, possibly flashbangs, and the sound of gunfire shortly before Texas governor Greg Abbott announced the crisis was over.

Britain’s foreign office confirmed the death of a British man in Texas, when asked to respond to a Sky News report that the gunman was a British national. The foreign office did not explicitly say the dead Briton was the gunman.

FBI negotiators had opened contact with the man, who said he wanted to speak to a woman held in a federal prison.

In the first few hours, the man could be heard having a one-sided conversation in what appeared to be a phone call during a Facebook livestream of the service of the Reform Jewish synagogue in Colleyville, which is about 26km northeast of Fort Worth. The livestream cut off around 3pm EST.

Before the livestream ended, the man could be heard ranting and talking about religion and his sister, the Fort Worth Star-Telegram reported. The man could be heard repeatedly saying he did not want to see anyone hurt and that he believed he was going to die, the newspaper said.

President Biden praised the “courageous work” of state, local and federal law enforcement in freeing the hostages.

A US official briefed on the matter told ABC News the hostage-taker had claimed to be the brother of Pakistani neuroscientist Aafia Siddiqui, who is serving an 86-year

US prison sentence for her 2010 conviction for shooting at soldiers and FBI agents, and that he demanded she be freed.

Siddiqui is being held at a federal prison in the Fort Worth area. A lawyer representing Siddiqui, Marwa Elbially, told CNN in a statement the man was not Siddiqui’s brother. He implored the man to release the hostages, saying Siddiqui's family condemned his “heinous” actions.

The Council on American-Islamic Relations (CAIR), a US Muslim advocacy group, condemned the man’s actions. “This latest anti-Semitic attack on Jewish Americans worshipping at a synagogue is an act of pure evil,” CAIR said.