London Tube attack latest: Arrest made as terror threat raised to 'critical'
ISIS has claimed involvement in the train blast but has offered no evidence to support the claim.
- UK terror threat level has been raised from "severe" to "critical," meaning an attack is expected imminently.
- Three of at least 30 people injured remained in a London hospital Saturday.
- ISIS said via its Amaq news agency that a "detachment" from the group had carried out the attack, but it gave no proof.
- Detectives have spoken with at least 45 witnesses and received scores of images from the public.
- More police were on patrol this weekend, in particular around "crowded places, iconic sites, transport hubs and ports," a police statement said.