British detectives investigating the Parsons Green Tube train bombing in London, have reportedly made a "significant arrest" in the case. The explosion on an underground train on Friday left at least 29 people injured.

The Islamic State (ISIS) group late on Friday claimed responsibility for the attack. A statement published by the terror outfit's Amaq propaganda agency said, "The bombing on a metro in London was carried out by a detachment of the Islamic State group.

The UK has raised its national threat level to "critical" suggesting another attack could take place. Prime Minister Theresa May has announced troops would be deployed in important sites, especially overcrowded places.

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Police officers walk on the road near Parsons Green tube station in London, Britain September 15, 2017.Reuters

Reports state the 18-year-old suspect was arrested by Kent Police in the port area of Dover on Saturday morning under section 41 of the Terrorism Act.

The suspect is currently in custody at a local police station. Reports state he will soon be transferred to a south London police station.

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An injured woman outside Parsons Green stationReuters

"We have made a significant arrest in our investigation this morning. Although we are pleased with the progress made, this investigation continues and the threat level remains at critical," Deputy Assistant Commissioner Neil Basu, Senior National Co-ordinator for Counter Terrorism Policing said.

"This arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage," Basu added. "The 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 extra armed officers remain in place."