One man died and 10 people were injured after a van drove into a crowd of Muslim worshippers near a mosque in London in the early hours of Monday.
London Mayor Sadiq Khan called it an "horrific terrorist attack" and counter-terrorism police are leading the investigation, as Muslim leaders linked the incident to a rise in Islamophobic crime.
Here is what we know so far:
Witnesses said a white van struck a crowd of Muslim worshippers who had been attending evening prayers during the holy month of Ramadan and were looking after a man who had collapsed.
Police said they were first called shortly after midnight.
Where did it take place?
The incident happened outside the Muslim Welfare House, 100 metres (yards) around the corner from the Finsbury Park Mosque. The mosque was once a notorious hub for radical Islamists that has since become a centre for inter-faith outreach.
The scene is just metres from the main railway line linking London with Edinburgh, the main Arsenal Football Club shop and what was the Rainbow Theatre, considered the prestige London concert venue in the 1960s and 1970s.
Who is the suspect?
The van's 48-year-old driver was detained by members of the public and then arrested by police on suspicion of attempted murder.
Witnesses said the man was white.
He has been taken to hospital as a precaution and is due to receive a mental health assessment.
Witness Khalid Amin told BBC television the man was shouting: "I want to kill all Muslims".
How many victims?
One man was pronounced dead at the scene and eight people were taken to hospital. Two others were treated at the scene for minor injuries.
Two of the injured are said to be in a serious condition.
The man who died was already receiving first aid at the scene. Witnesses said they saw him collapse shortly before the attack began.
"Any causative link between his death and the attack will form part of our investigation. It is too early to state if his death was as a result of the attack," police commander Neil Basu said.
Amateur video footage showed at least three people on the ground in the aftermath of the attack, with one man receiving mouth-to-mouth resuscitation.
Police said all the casualties were members of the Muslim community.
Why are many residents angry?
Many local Muslim worshippers complained that police did not immediately treat it as a terrorist attack, saying they would have treated the incident differently if it had been an Islamist assault.
Police issued an initial statement at 01:03 am (0003 GMT) saying a vehicle had collided with pedestrians.
In a statement at 04:46 am they said the incident was being investigated by counter-terrorism police.
Some people at the scene also complained that police took too long to arrive. One witness told the BBC he held down the suspect for 20 to 30 minutes before police arrived.
But the police said they had responded "instantly" as officers were in the immediate vicinity. They said additional officers arrived within 10 minutes.
How did Muslim groups react?
The Muslim Council of Britain umbrella group said it expected increased security "as a matter of urgency".
"Over the past weeks and months, Muslims have endured many incidents of Islamophobia and this is the most violent manifestation to date."
Following an Islamist-inspired van-and-knife attack in the London Bridge area on June 3, the city saw a sharp rise in anti-Muslim crimes.
On a single day -- June 6 -- 20 anti-Muslim incidents were reported, compared to a daily average of 3.5 incidents previously in 2017.
"The British Muslim community requires all decent people to stand with us against this evil violence," said Mohammed Shafiq, head of the Ramadhan Foundation community group.
"Rampant Islamophobia has been on the rise for a number of years".
How did politicians react?
Prime Minister Theresa May, who was criticised for her reaction to London's Grenfell Tower fire disaster last week, responded quickly, saying police were treating it as "a potential terrorist attack".
She was due to hold an emergency ministerial meeting on Monday.
Opposition Labour leader Jeremy Corbyn, who is the MP for the area, said he was "totally shocked".
Mayor Khan called it a "deliberate" and "horrific" terrorist attack on "innocent Londoners".