British police say a man has been arrested after an assault on police outside Buckingham Palace in central London.

"The man was stopped...at approximately 20:35 hours (1935 GMT) by officers at the Mall outside Buckingham Palace in possession of knife. Two male police officers suffered minor injuries to their arm," said a Metropolitan Police statement. No other injuries were reported.

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.The police confirmed Saturday that the attacker had a "four-foot sword" in his car.

Upon being challenged by officers, the 26-year-old attacker "reached for what we now know to be a four-foot sword which was in the front passenger foot well," the police statement said.

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.

Buckingham Palace is the home of Queen Elizabeth II but the queen usually spends August in Scotland at her Balmoral estate with family members.

Britain was hit by four militant attacks that killed 36 people earlier this year and the country's threat level is set at severe, meaning an attack is highly likely.