British police said a man had been arrested on suspicion of murder after three people were found dead on the street in the central English city of Nottingham on Tuesday and three were injured after an attempt to run them over with a van.
Detectives said they had an open mind about the motive for the linked incidents, which began just after 4 a.m. (0300 GMT), and added that counter-terrorism officers were working on the investigation, although they said this was normal.
Two of those killed were students from one of the city's universities. A 31-year-old man has been arrested on suspicion of murder and detectives said they were not looking for anyone else.
Two of those killed were students from one of the city's universities.
The major operation, which led to many roads across Nottingham being closed, began after police were called to a report of two people being killed on the road in the city center.
Officers were then alerted to another incident where someone driving a van had tried to run over three people, leaving one man in critical condition in hospital. At the same time, the other two suffered minor injuries.
Another man was then found dead shortly afterward on a road about two miles from the first incident.
"We are keeping an open mind as we investigate the circumstances surrounding these incidents and are working alongside Counter Terrorism Policing to establish the facts – as we would normally do in these types of circumstances," Chief Constable Kate Meynell said.
"We are at the early stages of the investigation and need to determine the motives behind these attacks and will keep the public updated as soon as we are able to say more."
The University of Nottingham said two of those killed were its students.
"We are shocked and devastated by the news and our thoughts are with those affected, their families and friends," the university said on Twitter.
Witness Lynn Haggitt told BBC TV she had seen a van hit a man and a woman who was left lying in the street.
"He went straight into these two people. The woman went on the kerb, the man went up in the air," she said. "There was such a bang. I wish I never saw it. It's really shaken me up."
Inside one of the police cordons, officers were guarding a white van with its passenger door wide open and a rucksack lying on the ground beside it. It had damage to its bonnet and windscreen.
At Ilkeston Road, where the two people were found dead, medical equipment was strewn across the street.
"I am being kept updated on developments. The police must be given the time to undertake their work," Prime Minister Rishi Sunak wrote on Twitter, calling the incident "shocking".
Several major roads around the city remained closed and the Nottingham tram network was suspended.
"Awful news for our city to wake up to today," Alex Norris, a lawmaker for Nottingham, said on Twitter. "Our community’s thoughts and prayers are with all those affected."