Pro-Islamic State accounts called upon followers to “hunt your prey” prior to Monday night’s explosions at the Manchester Arena, according to SITE Intelligence Group.

The accounts provided information on U.K. community centers, government buildings and tourist areas, according to SITE Director Rita Katz. No group has claimed responsibility for the attack. However, ISIS accounts have celebrated the incident on social media. British counter-terrorism authorities are reportedly treating the event as a “possible terrorist incident.”

Users on a pro-ISIS forum referred to the attack as “a successful and surprising blow” against the U.K. and considered it revenge for the country’s participation in air strikes in Iraq and Syria, according to Katz.

1) No claim regarding blast in #Manchester, but #ISIS accounts celebrating the attack, disseminating media & threats pic.twitter.com/Z8VqKWUkXD — Rita Katz (@Rita_Katz) May 23, 2017

A suicide bomber reportedly conducted the attack, which has killed at least 19 people and injured approximately 50 others, according to the most recent police reports. Two explosions outside a ticket kiosk sent nails flying into attendees. The use of nails and screws in bombs is a common tactic within jihadist groups.

The U.K. was on its second highest state of alert at the time of the event, meaning an attack was “highly likely.”

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