BRUSSELS (AFP) - Police in Belgium and Britain were on Saturday (Aug 26) investigating two knife attacks on security forces by assailants who allegedly shouted "Allahu akbar" before being stopped.

The attacker in Brussels, who wounded a soldier on Friday in what authorities said was an "attempted terrorist murder", was shot dead, while police in London overpowered a man who injured three unarmed officers outside Buckingham Palace with a metre-long sword.

The 26-year-old man has been arrested under the Terrorism Act, which allows for 14 days of pre-charge detention, and is being held at a police station in central London.

The two incidents come as much of Europe is on high alert following a string of major attacks over the past two years - most of which have been claimed by Islamic militants.

Last week, Spain was hit by twin vehicle attacks which left 15 dead, and two people were killed in a stabbing spree in Finland.

Belgian prosecutors said the attacker yelled "Allahu akbar" (God is greatest) during the assault before being shot by a soldier in the centre of city, which has been on high alert since last year's carnage at the airport and on the metro.

One of the soldiers was slightly hurt in the attack which Brussels Mayor Philippe Close said had been carried out by a "lone individual".

Overnight, police raided the suspect's home in Bruges, north-west Belgium.

'METRE-LONG SWORD'

During the attack near the Grand Place in central Brussels at 8pm, the man rushed at several soldiers from behind and struck them with a knife, prompting one of them to open fire.

"The man was hit and died shortly afterwards in hospital from his wounds," the prosecutors' statement said. As well as the knife, police found a replica gun and two copies of the Quran on him.

The assailant was a Belgian national of Somali origin who was born in 1987, authorities confirmed. He arrived in the country in 2004 and was granted Belgian nationality in 2015.

Although not known for any terror-related activities, he had an assault and battery charge on his record from February, the statement said.

Less than two hours later, a man drove his car at a police van outside Buckingham Palace.

The attacker "repeatedly shouted Allahu akbar", reached for a metre-long sword and had to be incapacitated with CS gas, police said in a statement on Saturday.

Three officers were slightly injured in the incident.

No members of the royal family were in the residence at the time of the attack.

The man's identity has not been disclosed but police said he was from Luton, a city 50km north of London.

"Officers from the Counter Terrorism Command are now investigating and searches are being carried out in the Luton area today," the police said in a statement.

"We believe the man was acting alone and we are not looking for other suspects at this stage."

With much of Europe on edge over the attacks, many of them low-tech assaults using knives or vehicles as weapons, thousands of people took to the streets of Barcelona on Saturday in a defiant march under the slogan "No tinc por" - Catalan for "not afraid".

'SOLDIER BLEEDING'

The Brussels attack happened on a boulevard near the Grand Place central square, one of the "sensitive" areas of the capital where armed soldiers are on patrol because of the terror threat.

"I heard yelling and straight away two shots," a witness called Yohan told AFP. He did not wish to give his surname.

As he approached, he said he saw "a soldier bleeding from his hand and a man on the ground," who had a beard and was wearing a hood.

Soldiers have been deployed at railway stations and landmark buildings in the Belgian capital since the November 2015 attacks on Paris when investigators found the assailants had a clear link with Brussels.

Patrols has been stepped up since suicide bombers struck Zaventem Airport and Maalbeek metro station in March 2016, killing 32 people and wounding hundreds more.

The carnage in Paris, which left 130 people dead and hundreds more wounded, was claimed by the Islamic State in Iraq and Syria (ISIS) group, which also said it was behind the bombings in Brussels.

In June, a man who tried to bomb a Brussels Central train station was shot dead by a soldier.

In Britain, 35 people have been killed in three jihadist attacks in London and Manchester since March.