LONDON • A car mounted a sidewalk outside London's Natural History Museum yesterday, injuring several pedestrians in an incident which British police have not ruled out as terrorism.

Armed police were at the scene, and a video posted on Twitter showed a man being held down on the road next to a black car that appeared to have crashed.

London's Metropolitan Police described the incident in the South Kensington area of west London as a collision and said the motive for the incident was under investigation. "Inquiries to establish the circumstances and motive are under way," police said on Twitter.

A spokesman for the London police force later said that counter-terrorism officers were assessing the incident but had not yet reached a conclusion, but police are keeping an open mind as to whether it is terrorism-related.

Police originally said a man was arrested at the scene, but later clarified that he had only been detained.

One witness, who gave his name only as Leonard, said: "I was near South Kensington station and there were many police officers.

"Suddenly a female police officer shouted at the crowd to run, and everybody ran in panic, many people were screaming."

A BBC reporter at the scene said she could see a car had stopped diagonally across the road, surrounded by a crowd of people with one or two on the ground. She said she was told by the police that the victims' injuries were minor.

The museum said on Twitter that it was working with the police after "a serious incident" outside the museum and would provide more information later.

Britain is on its second-highest security alert level, meaning that an attack by militants is considered highly likely. There have been five attacks described by the authorities as terrorism this year, three involving vehicles.

In March, a man drove a car into pedestrians on London's Westminster Bridge, killing four people before stabbing a police officer to death in the grounds of Parliament.

In June, three Islamist militants drove into pedestrians on London Bridge and then stabbed people at nearby restaurants and bars, killing eight.

The Natural History Museum is the fourth-most popular tourist attraction in Britain, with 4.6 million visits last year, according to the Association of Leading Visitor Attractions.

REUTERS, AGENCE FRANCE-PRESSE