Shots have been fired by firearms officers in the Holland Park area of west London, the Metropolitan police have said. "The culprit was apprehended and taken to a police station", the embassy said in a statement.
In a statement on their website, the Ukrainian embassy said the vehicle was "deliberately rammed".
"The police were called immediately, and the suspect's vehicle was blocked up", it added.
London's Metropolitan Police confirmed they were called to reports of a auto hitting a number of parked cars near the Ukrainian embassy.
Officers opened fire in west London on Saturday morning while responding to reports of a vehicle collision, the Metropolitan Police has said. "The police are investigating the suspect's identity and motive for the attack".
Officers used firearms and a Taser before arresting a man in his 40s.
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Firearms officers swooped and the vehicle was then driven at police.
The vehicle has been a focus of attention for forensics officers.
The vehicle, which a police source said was a Mercedes, appeared to have been backed into the black auto.
Some reports suggested there were shots from the auto that hit the ambassador's vehicle, but the embassy said only the British police opened fire.
The black vehicle was heavily scuffed on its right-hand side.
The Met said officers were called at approximately 8.30am to reports of a vehicle in collision...
Officers have remained at the scene during the day, with a silver Mercedes vehicle pictured parked across a street with its boot open and damage to the driver-side front window.