(NewsNation Now) — The FBI and the Department of Homeland Security warned in a letter Monday that faith-based communities will likely remain targets for violence, according to a letter obtained by CNN. Officials have urged state and local leaders to access their security postures for mass gathering events and churches.

The alert comes days after 44-year-old British national Malik Faisal Akram took four people hostage at a Texas synagogue for 10 hours on Saturday.

Rabbi Charlie Cytron-Walker and three other men were participating in the service that was being livestreamed when they were taken hostage. One of the four hostages held at Congregation Beth Israel in Colleyville was released during the standoff; three others were rescued when authorities entered the building about 9 p.m., authorities said.

Akram was shot and killed on the scene. The FBI and police did not say who shot him. An investigation into the incident continues.

The FBI on Sunday night issued a statement calling the ordeal “a terrorism-related matter, in which the Jewish community was targeted” and said the Joint Terrorism Task Force is investigating. President Joe Biden called the episode an act of terror. 

The agency noted that Akram spoke repeatedly during negotiations about a prisoner who is serving an 86-year sentence in the U.S. Akram could be heard ranting on a Facebook livestream of the services and demanding the release of Aafia Siddiqui, a Pakistani neuroscientist suspected of having ties to al-Qaida who was convicted of trying to kill U.S. Army officers in Afghanistan.

Siddiqui is in custody at a federal prison in Texas, but it is unclear why Akram chose the Colleyville synagogue.

FBI Special Agent in Charge Matt DeSarno said the hostage-taker was specifically focused on an issue not directly connected to the Jewish community.

Officials say he arrived in the U.S. on a tourist visa from Great Britain the first week of the new year and stayed in area homeless shelters in the two weeks leading up to the attack.

Former CIA operative Mike Baker said lone wolf attackers are always going to be an issue.

“No matter what their ideology is, no matter what their mental health state is. It’s a heavy lift at all times for law enforcement and for the intel community,” said Baker.