A man was arrested on Friday after attacking police with a knife outside Queen Elizabeth II's Buckingham Palace residence in London, police said.
"The man was stopped... at approximately 20:35 hours (1935 GMT) by officers outside Buckingham Palace in possession of knife," said London police statement.
Two male police officers suffered minor injuries to their arm and the man was arrested on suspicion of grievous bodily harm and assault.
The officers were treated at the scene and did not require hospital treatment, according to police, who said it was too early to say whether the attack was terrorism.
However, social media users reported that the attacker was armed with a sword, and posted videos of a fleet of police cars and ambulances outside the world-famous palace, with the surrounding roads sealed off.
Twitter user Amir Jan Malik wrote: "Stuck outside Buckingham palace with many armed police officers. Heavy rifles on display traffic at a halt."
Eyewitness Kiana Williamson told the Press Association that "there was one police van and one car, there was also a civilian's car that had veered towards the police car.
"They were trying to get the man out of the car, shouting, more police were arriving on to the scene and the man was fighting back," she said.
"The man had been restrained and looked almost unconscious by the side of the road.
"I didn't see the car driving but the car had been left at the side of the road and an eye witness had said that he had driven towards the police car," she added.
The incident occurred just two hours after a knifeman attacked two soldiers in Brussels in what authorities are treating as a terrorist attack.
The Queen is at her Balmoral residence in Scotland, although the palace said it would not comment on security issues.