Police were negotiating with a man believed to have taken people hostage at a synagogue in Colleyville, Texas, during a religious service on Saturday that was being broadcast online.

The Colleyville Police Department said FBI negotiators remained in contact with the hostage taker late Saturday afternoon, after a male hostage was released uninjured more than six hours after the crisis began.

Other hostages were still being held.

The police said it had evacuated residents from the area around Congregation Beth Israel as it deployed SWAT teams after responding to an emergency call at 10:41 a.m. No injuries have been reported and it remained unclear what weapons, if any, the man had.

There were initially four hostages, including the rabbi, according to a person familiar with the situation who was not authorized to speak publicly.

The man could be heard having a one-sided conversation in what appeared to be a phone call during a Facebook livestream of the Shabbat service of the Reform Jewish synagogue in Colleyville, which is about 16 miles (26 km) northeast of Fort Worth. The livestream cut off around 3 p.m. EST (2000 GMT).

Before the livestream was 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 didn't want to see anyone hurt and that he believed he was going to die, the newspaper said.

President Joe Biden has been briefed on the "developing hostage situation," his press secretary said. Israeli Prime Minister Naftali Bennett said on Twitter that he was monitoring the situation and was praying for the safety of the hostages.

Texas Governor Greg Abbott said officials from the state's Department of Public Safety were also on the scene working to get "the best and safest outcome."

Barry Klompus, a member of the congregation since it opened in 1999, said he tuned into the livestream.

"It was horrible listening and watching, and it's that much more horrible not knowing," Klompus said in a telephone interview.

Though he was not able to clearly understand what the man wanted, Klompus believed the man wanted to talk to his sister.

A U.S. official briefed on the matter told ABC News the hostage-taker claims to be the brother of Pakistani neuroscientist Aafia Siddiqui, who is serving an 86-year U.S. prison sentence on her 2010 conviction for shooting at soldiers and FBI agents, and demanding she be freed.

But authorities have not yet confirmed his identity, the official told ABC News.

Siddiqui is being held at a federal prison in the Fort Worth area.

The president of the Union for Reform Judaism, Rabbi Rick Jacobs, said on Twitter the union was "very grateful to law enforcement who are working to free the hostages." The Anti-Defamation League, a Jewish advocacy group, said it was aware of the standoff, and the Council on American-Islamic Relations (CAIR), a U.S. Muslim advocacy group, condemned the man's actions.

"This latest antisemitic attack on Jewish Americans worshipping at a synagogue is an act of pure evil," CAIR said in a statement.

Klompus said he did not know of any significant previous threats to the congregation.

"We don't have a security officer on staff but we have what I would say is a very good relationship with the local police," he said.