At least four hostages were being held at a Texas synagogue by a man demanding the release of a Pakistani neuroscientist convicted of trying to kill US army officers in Afghanistan.
The Colleyville Police Department tweeted on Saturday afternoon it was conducting Swat operations at the address of Congregation Beth Israel, north-east of Fort Worth.
At least four hostages, including a rabbi, were believed to be inside the synagogue, according to two law enforcement officials who were not authorsed to discuss the ongoing investigation and who spoke to The Associated Press on the condition of anonymity.
Authorities are still trying to discern a precise motive for the attack.
The hostage-taker was heard demanding the release of Aafia Siddiqui, a Pakistani neuroscientist suspected of having ties to al-Qaeda, who was convicted of trying to kill US military officers while in custody in Afghanistan, the officials said.
He also said he wanted to be able to speak with her, according to the officials. Siddiqui is in federal prison in Texas.
The officials said investigators have not positively identified the man and cautioned that the information was based on a preliminary investigation as the situation was still rapidly developing.