(AP) — British Transport Police says armed officers will patrol some U.K. trains for the first time because of the increased threat of extremist attacks.

The patrols will begin Thursday afternoon.

Officials say the plan is to “ensure that the travelling public are kept safe on the rail network.”

Armed officers have patrolled London Underground subway trains since December, but the move announced Thursday expands the security measure to train services elsewhere in the country.

British Transport Police Chief Constable Paul Crowther says the force has “radically increased” its presence since the Monday night attack in Manchester.