Last updated at 2:08 p.m.

POLITICAL JOURNALISTS AND BYSTANDERS in London watched in horror as a police officer was stabbed outside the House of Commons on Wednesday afternoon, and the suspected assailant then ran towards the door used by members of Parliament to enter the chamber before being gunned down by plain clothes officers.

Both the attacker and the officer later died of their wounds, along with at least two bystanders who were run down by the suspected assailant’s car on Westminster Bridge outside Parliament. Witness accounts of the attack were quickly shared on social networks.

Quentin Letts, a Daily Mail politics writer, told the BBC he saw a man in black using what appeared to be a knife to attack a police officer close to Big Ben, before being shot as he rushed towards the entrance to Parliament.

Radoslaw Sikorski, Poland’s former foreign minister, shared video of bystanders rushing to help wounded people on the bridge in the immediate aftermath of the attack.

David Lidington, the leader of the House of Commons, confirmed that the attacker was shot and killed on the grounds of Westminster Palace. Parliament was suspended and the members were forced into lockdown after the incident.

Tobias Ellwood, a former soldier who is now a member of Parliament and Foreign Office minister, was among those who tried to save the life of the wounded officer.

Video of that scene was captured by Jaden Patel, a bystander, who shared the images online.

As the area around Parliament was sealed off, and first responders attempted to treat the wounded, political journalists shared fragmentary glimpses of the scene.

The Metropolitan Police said that they were “treating this as a terrorist incident until we know otherwise,” and armed officers were on the scene.

The police also appealed to the public to show “restraint” in what images they share online.

Among those showing no restraint, and instead seeking to capitalize on the raw emotions following the attack, was the anti-Muslim extremist Tommy Robinson, a hero of Breitbart News, who rushed to the scene of the crime to rant about it being part of a 1400-year war between Islam and the West.

While Robinson is a fringe figure in Britain, the attack could play a role in the upcoming presidential election in France, given that the French prime minister confirmed that some of those injured by the car were schoolchildren from Brittany. Marine Le Pen, the far-right, anti-Muslim candidate for the presidency, quickly released a statement on the attack.