British Prime Minister Theresa May says the threat level in the UK has been raised to "critical" – meaning another terrorist attack is feared to be "imminent."
It follows Monday night's suicide bombing in Manchester in which 22 people were killed at the end of a pop concert.
"It is now concluded on the basis of today's investigations that the threat level should be increased from severe to critical," May said.
"This means the assessment is not only that an attack is highly likely but that a further attack may be imminent," she added.
TRT World 's correspondent Jon Brain reports with more from Manchester.