Two teenagers have been arrested in England as part of the investigation into a hostage-taking incident at a synagogue in Texas on Saturday.
British citizen Malik Faisal Akram, 44, from Blackburn, was shot dead after a standoff with police in Colleyville.
Details of the ages or genders of the pair arrested in south Manchester on Sunday evening were not revealed.
Greater Manchester Police said it was liaising with local communities and continuing to assist in the US inquiry.
The force said the two teenagers were arrested “as part of the ongoing investigation into the attack” and were being held in custody for questioning.
Home Secretary Priti Patel said she had offered “the full support” of the UK police and security services in the investigation when she spoke to her US counterpart, Alejandro Mayorkas, on Monday.
She told MPs there were a range of measures being undertaken in the UK in response, “including protective security for the Jewish community”.
Texas synagogue hostage-taker was British
According to US police sources, Akram arrived in the country via New York’s JFK International Airport two weeks ago and he is believed to have bought a handgun used in the incident after his arrival.
Akram’s brother Gulbar confirmed his death in a statement carried on the Blackburn Muslim Community’s Facebook page. He apologised to the victims and said his brother had been suffering from mental health issues.
The Metropolitan Police earlier confirmed counter-terrorism officers were in contact with US authorities and the FBI.
The siege began at around 11:00 local time (16:00 GMT) when police were called to the Congregation Beth Israel synagogue in the suburb of Dallas.
Neighbours told the BBC they heard a commotion when armed police were sealing off the area, followed later by a loud bang, which shook their house.
Suzanne Hughes said she was at home celebrating a birthday with her family when they saw police with guns drawn rush towards the synagogue.
“I was expecting the synagogue to have exploded – it had not, but it was very unnerving. We heard gunfire when we got to the backyard.
“It’s sad. This is America. You’re supposed to be able to be safe everywhere you go,” she added.
Akram gained initial access to the synagogue during the service by claiming to be a homeless man, according to a police source quoted by CBS.
Among the hostages was the synagogue’s rabbi. One was released after six hours with the other three being led to safety by police several hours later.
All of the hostages at the synagogue were freed unharmed.
Rabbi Charlie Cytron-Walker told CBS the hostages were “terrified” and described how he threw a chair at the gunman as they made their escape “without even a shot being fired”.
US President Joe Biden called the hostage-taking an “act of terror”, and UK Foreign Secretary Liz Truss described it as an “act of terrorism and anti-Semitism”.
Ms Truss said in a tweet: “We stand with US in defending the rights and freedoms of our citizens against those who spread hate.”
This FBI-led investigation is likely to spread across three continents, focussing primarily on what is known about hostage-taker Malik Faisal Akram here in the UK, as well as anyone who may have helped him, either in the UK or the US.
His reported demand for the release of convicted Pakistani neuroscientist Aafiya Siddiqui from a US jail has given this a further dimension which will undoubtedly lead to contact between the FBI and the authorities in Pakistan.
Akram’s choice of a Jewish synagogue for the siege has already prompted a statement from Israeli Prime Minister Naftali Bennett, warning of the need to fight anti-Semitism.
But for now the immediate focus is on anyone Akram was in contact with in the area of north-west England where he came from.
That brings in MI5, the security service, Counter Terrorism Policing North West and Greater Manchester Police.
There has been no confirmation yet of whether Akram was already known to the UK authorities but he had no prior police record in the US.
The hostage-taker was heard demanding the release of Aafia Siddiqui, a Pakistani neuroscientist jailed over attempts to kill US soldiers in Afghanistan, law enforcement officials told local media.
Officials added Akram also asked to speak to Siddiqui, who is serving an 86-year term in a prison in Forth Worth, Texas, about 20 miles away from the synagogue. Siddiqui has distanced herself from his actions, issuing a statement through a lawyer.
President Biden appeared to confirm the attacker had been seeking her release, saying the Texas attack was related to “someone who was arrested 15 years ago and has been in jail for 10 years”.
The president said while he did not have all the details it was believed Akram had “got the weapons on the street”, saying he had “purchased them when he landed”, but he added there were “no bombs that we know of”.
He also said Akram was thought to have spent his first night in a homeless shelter.
Police sources said US federal courts did not show he had any criminal history.
Akram’s brother said he had liaised “with Faisal, the negotiators, FBI etc” during the siege but “there was nothing we could have said to him or done that would have convinced him to surrender”.
Gulbar added: “We would like to say that we as a family do not condone any of his actions and would like to sincerely apologise wholeheartedly to all the victims involved in the unfortunate incident.
“We would also like to add that any attack on any human being be it a Jew, Christian or Muslim etc is wrong and should always be condemned.”
The Muslim Council of Britain (MCB) has expressed solidarity with the Jewish community following the hostage-taking, describing it as “completely unacceptable”.
Zara Mohammed, secretary general of the MCB said: “The act is all the more reprehensible since it was instigated at a place of worship where Jews were targeted.
“This was, quite simply, a hate crime and an act of anti-Semitism.”