Exact motivations behind the vehicle and knife attack outside Parliament in London remain unclear, but observers have noted that the incident occurred on the anniversary of the multiple Islamist attacks on the Belgian capital on March 22, 2016.

“These incidents are obviously very concerning indeed, coming as they do on the first anniversary of the Brussels terror attacks,” Tom Elliott, an Ulster Unionist MP, told the Belfast Telegraph.

Wednesday’s attack appeared to happen in several stages: at first a car reportedly mowed down multiple pedestrians on Westminster Bridge, before crashing into the perimeter of the Parliament building.

David Lidington, the leader of the House of Commons, said that in the aftermath a policeman had been stabbed, the assailant was shot dead, and there were “further violent incidents in the vicinity.”

MPs had to be placed under lockdown, while Prime Minister Theresa May was evacuated from Westminster.

The Brussels attack last year followed a different format, but both incidents share features of recent jihadist attacks, while terrorists have also often chosen significant dates and anniversaries to carry out their plans.

Today's attack in London falls on the 1-year anniversary of the Brussels attack (could be a coincidence). — Max Abrahms (@MaxAbrahms) March 22, 2017

Recall: Brussels terrorist attack happened exactly one year ago today. Terrorists are notorious for using significant dates. #London — Nick Short (@PoliticalShort) March 22, 2017

The Brussels attack consisted of three coordinated suicide bombings by three Belgian-Moroccan citizens, two in the city’s airport, and one in the central Maalbeek metro station, occurring one hour afterwards.

Thirty-two victims and three perpetrators were killed in the attack, and more than 300 injured.

The organizers, several of whom did not participate directly, had criminal records, and several had traveled to Syria to fight for Islamic State (IS, formerly ISIS/ISIL), or were under the influence of radical preachers in Europe.

Shortly before the violence unfolded in London, Belgium's King Philippe urged listeners at a packed memorial service in Brussels to “make our society more humane, and more just,” and called for individuals to “dare to be tender.”

Despite the similarity in dates, the format of the London attack was more reminiscent of the Nice truck attack in France, when 86 people on a promenade were hit with a truck and shot by an Islamist during Bastille Day celebrations in July last year. While invented in the 20th century, the tactic has been specifically advocated by jihadist terror manuals, and copycat attacks have taken place in the past year in Berlin, Jerusalem and Ohio.