Nineteen people have been killed in a suspected terrorist attack during a pop concert by US star Ariana Grande in the northwest English city of Manchester, police say.

Police officers laid flowers as a tribute to the officer Keith Palmer who lost his life in the terror attacks in London this week. Rough cut (no reporter narration).

A 'significant' Islamic State-inspired Christmas Day terror plot targeting central Melbourne with explosives has been foiled after a series of arrests in raids across the city, police say.