The United Kingdom's counterterrorism police have said the teenagers were detained in South Manchester and remain in custody for questioning.
Two teenagers have been detained in South Manchester as part of an ongoing investigation into a hostage-taking incident at a synagogue in the US state of Texas.
The UK's counterterrorism police said on Sunday the teenagers were detained in connection with the hostage-taking incident by a British national in Texas over the weekend.
"Two teenagers were detained in South Manchester this evening. They remain in custody for questioning," the Greater Manchester Police said in a statement.
The arrests came after the US Federal Bureau of Investigation (FBI) identified the hostage-taker as British national Malik Faisal Akram, 44.
Previously, Matthew DeSarno, special agent in charge of the FBI's Dallas Field Office, said the captor acted alone with no other involved in the January 15 hostage-taking.
Britain on Monday promised "full support" to US investigators.
"This was a terrible and anti-Semitic act of terrorism," Prime Minister Boris Johnson's spokesman told journalists after Akram was killed.
Four people, including a rabbi, were held by gunman Akram who entered the Congregation Beth Israel synagogue in Colleyville during a religious service.
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 Qaeda who was convicted of trying to kill US Army officers in Afghanistan.
After hours of a standoff with law enforcement, all hostages were freed, the police said, adding the captor was killed in a shooting incident.
The standoff led authorities to tighten security in other places, including New York City, where police said that they increased their presence “at key Jewish institutions” out of an abundance of caution.