COLLEYVILLE: All four people taken hostage in a more than 10-hour standoff at a Texas synagogue have been freed unharmed, police said late Saturday, and their suspected captor is dead. The suspect was apparently demanding the release of Dr Aafia Siddiqui, a Pakistani neuroscientist jailed in the US for almost a decade.

Some 10 hours into the crisis, state governor Greg Abbott tweeted that "all hostages are out alive and safe" at 9:30 pm (0330 Sunday GMT).

Colleyville police chief Michael Miller told a news conference that a "rescue team breached the synagogue" on Saturday evening and rescued the three remaining hostages -- all adults -- being held inside.

A first hostage had been released unharmed a few hours earlier. "The suspect is deceased," Miller told reporters.

FBI Dallas Special Agent Matt DeSarno said the four hostages did not need medical attention and would soon be reunited with their families.

"He did not harm them in any way," he said.

There were reports from journalists at the scene of a loud explosion and gunshots at the synagogue just before Abbott had made the announcement.

With reports the synagogue's rabbi was among at least four being held, the standoff sparked an outpouring of concern from Jewish organisations around the United States, as well as from the Israeli government.

The Council on American-Islamic Relations (CAIR), a US Muslim advocacy group, also condemned the man's actions, reported Reuters.

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

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President Joe Biden had also been briefed on the hostage situation, according to the White House.

Police said they were alerted to an emergency Saturday morning at the Congregation Beth Israel in Colleyville, some 25 miles (40 kilometers) west of Dallas, with reports circulating quickly that it was a hostage situation.

ABC News reported that the hostage-taker was armed and had claimed to have bombs in unknown locations.

Quoting a US official briefed on the matter, ABC reported the man was demanding the release of Aafia Siddiqui.

ABC initially said the man claimed to be Siddiqui's brother, but then later clarified her brother is in Houston. Other experts said the word the man used in Arabic was more figurative and meant "sister".

Dr Aafia Siddiqui's lawyer says she 'has absolutely no involvement'

Aafia Siddiqui's lawyer said she "has absolutely no involvement" in the hostage situation in a statement to CNN. The lawyer confirmed that the man was not Siddiqui's brother and said she condemned his actions.

Siddiqui, a former Pakistani scientist, was in 2010 sentenced by a New York court to 86 years in prison for attempted murder of US officers in Afghanistan. The high-profile case sparked outrage in Pakistan.

She is currently being held at Federal Medical Center (FMC) prison in Fort Worth, Texas.

FBI on scene

A live stream of the congregation's Shabbat morning service, available on Facebook for around four hours during the standoff, appeared to capture audio of a man talking loudly -- although it did not show the scene inside the building.

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In it, 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."

Colleyville police said in a tweet at 11:30 am that it was "conducting SWAT operations" at the address of the Congregation Beth Israel.

FBI agents were also on the scene, according to an AFP journalist, as were Colleyville fire and rescue trucks, Dallas police and police from the nearby city of Southlake.

'Horrifying'

Beth Israel congregation member Ellen Smith, who grew up going to the synagogue, described the situation as "shocking and horrifying" in a CNN interview.

Israeli Prime Minister Naftali Bennett said Israel was monitoring the situation and praying for the hostages' safety.

Rabbi Joseph Potasnik, the executive vice president of the New York Board of Rabbis, said he was grateful to have received calls from people of all religious backgrounds expressing concern and hope for a peaceful outcome.

But he warned that the violence would not stop with the synagogue.

"The person who hates me today is going to hate you tomorrow. So it may start with Jews. It doesn't stop with Jews," he told CNN.