London train blast: The Kent Police in Dover arrested an 18-year-old in connection with London blast that took place at the Parson Green station on Friday. "We have made a significant arrest in our investigation this morning," Neil Basu, Senior National Co-ordinator for Counter Terrorism Policing, said in a statement. "Although we are pleased with the progress made, this investigation continues and the threat level remains at critical," as per PTI report.\u00a0The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation. We are not, at this time, changing our protective security measures and the steps taken to free up\u00a0extra armed officers remain in place," he added. As per reports, some were badly burnt due to the fireball that flew down the carriage in the terror attack. The bomb was hidden in a plastic bucket inside a supermarket freezer bag that went off at rush hour. Meanwhile, Deputy Assistant Commissioner Neil Basu, the senior national coordinator for CT policing, declared it to be a terrorist incident. The bomb was placed in a white bucket in a train full of passengers and was attached to a timer, as per Sky News report. This is the fourth incident that took place this year. UK Prime Minister Theresa May took to Twitter to express her condolences and said,\u201d My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident.\u201d The UK PM also chaired an emergency meeting following the incident. As per the report, the Met\u2019s assistant commissioner Mark Rowley said a suspected improvised explosive device (IED) was thought to be responsible for the blast. The report added, a circuit board was recovered from the scene. Scotland Yard\u2019s counter-terrorism command, SO15, has taken the lead in the investigation, supported by MI5. The inquiry into the explosion was initially led by BTP. Meanwhile, US President, Donald Trump blamed the explosion on \u201closer terrorists\u201d and called for a \u201cproactive\u201d response by security services.