A man wielding a knife was shot dead Friday after wounding a soldier in Brussels in a suspected "terrorist attack" while in London counter-terror detectives were investigating a similar attack on police near Buckingham Palace.

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

"We believe it is a terrorist attack," said a spokeswoman for the prosecutors' office.

The attack took place around 8:00 pm (1800 GMT) and Belgian media said the assailant was about 30 and of Somali origin.

Less than two hours later, two British police officers were slightly injured while arresting a man with a large knife outside Buckingham Palace in London.

The 26-year-old attacker, who was initially detained on suspicion of causing grievous bodily harm and assaulting police, was later arrested under the Terrorism Act 2000.

"Detectives from the Metropolitan Police's Counter Terrorism Command are now investigating the incident," police said.

The queen was at her Balmoral residence in Scotland at the time.

- Two shots -

The incidents follow vehicle attacks claimed by the Islamic State group in Spain last week which killed 15 people and another stabbing spree in Finland which left two dead and eight wounded.

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, or blamed on, jihadists.

One of the two soldiers targeted in Brussels was "slightly" wounded, according to federal prosecutors, who have opened a terror probe.

"All our support for our military," tweeted Belgian Prime Minister Charles Michel. "Our security services remain attentive, we are monitoring the situation closely with the Crisis Center," he added.

City mayor Philippe Close told reporters the incident was the work of a "lone individual".

"I heard yelling and straight away two shots," a witness named Yohan told AFP, who 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.

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

- Troops on streets -

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 Brussels.

Their presence has been reinforced since suicide bombers struck Zavantem 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 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.

No one was injured but officials said the consequences could have been severe if the bomb, which was packed nails and gas canisters, had detonated.

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

Two of those involved a vehicle ploughing into pedestrians.

The other attack was a bombing in May at the end of a pop concert by US star Ariana Grande in Manchester which killed 22 people, a third of them children

Source: AFP