In the United Kingdom, an 18-year-old man was arrested today in connection with the terror attack on a packed London Tube train. <br/><br/>The Metropolitan calling it a significant development in the ongoing investigation said, the man was arrested by Kent Police in the port area of Dover this morning under the UK's Terrorism Act. <br/><br/>He was taken into custody at a local police station and then transferred to a south London police station. Police Deputy Assistant Commissioner Neil Basu, also the UK's Senior National Co-ordinator for Counter Terrorism Policing, indicated that the force was still on the hunt for further suspects.<br/> <br/>Meanwhile, The Islamic State group has said it was behind the bomb but Met Police's Assistant Commissioner Mark Rowley said it was very routine for ISIS to claim the attack, whether in<br/>contact with those involved or not. <br/><br/>Announcing the change in the UK threat level, Prime Minister Theresa May said the military would be providing support to police and would replace officers on guard duty at national infrastructure sites not accessible to the public.