Police opened fire on a vehicle outside the Ukrainian embassy in west London after the driver deliberately and repeatedly rammed into the official car of the country's UK ambassador.
An official statement from the embassy said officers were called to the scene in the Holland Park area on Saturday morning and attempted to block the offending vehicle, but it continued to hit the car parked outside.
It was also driven at police officers, which the embassy said forced them "to open fire on the perpetrator's vehicle".
Onlookers described seeing officers armed with sub-machine guns and a suspect being "wrestled" to the ground.
Scotland Yard confirmed that a man in his 40s was arrested at the scene on suspicion of the attempted murder of police officers and criminal damage.
He was taken to a central London hospital as a precaution, following the use of firearms and a Taser.
The ambassador, Natalia Galibarenko, was not at the embassy at the time and no other staff were injured.
Police said the man they arrested also suffered no injuries and that the incident is not being treated as terror-related.
A neighbour who witnessed the arrest believes the suspect reversed into the ambassador's car while backing away from an oncoming police car.
Emma Slatter, who is Visa's general counsel, said: "It seems like he was moving erratically or wanting to move away from being boxed in, maybe not realising there were police behind him as well.
"That was when he collided backwards.
"I think I heard about half a dozen shots."
Two other witnesses said that they believed the suspect was Caucasian.
Heather Feiner, a mother-of-two, originally from the US, said: "My kids were hanging out in the living room. They said, 'Mum, is that firecrackers?'
"I saw all this police activity. I thought, 'Oh my gosh, what's going on?'"
She added that there were four marked police cars outside by the time she reached her ground floor window.
"From the time I heard the shots until I got to the window, which took about 15 seconds, all these police cars were already there," she said.
"I'm wondering if they were already trying to stop this person.
"I could see a police officer that fired the shots. I could see them pointing their gun at the car.
"They had a guy on the ground. I think he was Caucasian."
Another resident in the street, Lois Saint-Pierre, 89, said she had seen a Caucasian suspect.
"I heard the gun go off twice and then they wrestled him (the suspect) to the ground," she said.
Chief Superintendent Andy Walker, from the Met's specialist firearms command, said: "As is standard procedure, an investigation is now ongoing into the discharge of a police firearm during this incident.
"While this takes place, I would like to pay tribute to the officers involved this morning who responded swiftly to this incident and put themselves in harm's way, as they do every day, to keep the people of London safe."
Officers have remained at the scene during the day, with a silver Mercedes car pictured parked across a street with its boot open and damage to the driver-side front window.
The vehicle has been a focus of attention for forensics officers.
Meanwhile, the directorate of professional standards, which investigates complaints against the professional conduct of officers in the Met, has been informed of the incident.
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