One woman has been killed and up to six other people have been injured in a knife attack in central London.
The attack took place late on Wednesday night (local time) in Russell Square, city's Metropolitan Police said in a statement.
"Terrorism is one possibility being explored at this stage," it said, adding that extra officers remain in the area as a precaution.
Police confirmed that six people are injured in the attack, while one woman was killed.
A male suspect has been arrested for the attack, it said.
Eyewitnesses have reported a police forensics tent has been erected on Southampton Row, outside the park in the centre of the square, which is close to the British Museum.
There is a heavy police presence in the area and the initial cordon around the crime scene has been extended.
The condition of those injured and the extent of their injuries is not known at present.
One of the July 7, 2005, bombings, which killed 52 people in London, was on a bus in Tavistock Square, near Russell Square, which is home to an annual commemoration of the attacks.
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