(CN) At least 22 people were injured in London Friday morning when what police are describing as a crude device was exploded on a crowded commuter train.
The National Health Service said 18 people had been taken to hospitals and that another four had sought medical treatment on their own.
The bombing occurred at about 8:20 a.m. as the train was pulling out of the Parsons Green station in Southwest London.
Assistant Commissioner Mark Rowley of the Metropolitan Police, a top counter terrorism official, said at a news conference that the bomb was an improvised explosive device, and he urged anyone who had seen what happened, or had taken photos or videos of the incident, to come forward.
None of the injuries reported thus far are considered life-threatening.
The authorities immediately beefed up security around the London Underground, as the investigation into who was behind the bombing continues.
Friday incident was the fifth significant attack to occur in Britain this year. In March the country witnessed a vehicular and knife attack near Parliament, and then in May, a suicide bomber killed 22 people and wounded 59 others at an Ariana Grande concert in Manchester. The most recent attack before Friday was a van and knife attack on London Bridge in June.
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