A London Metropolitan Police officer has died, along with three others, in a brutal terrorist attack at the Palace of Westminster that appears to be the work of a lone assailant who was shot and killed by law enforcement officials.

Scotland Yard did not confirm the attacker's identity but did confirm that he was killed during the assault. Police said the man acted alone in the attack.

Met Police have confirmed that four people have died in the incident, which took place outside the Houses of Parliament in the center of London at around 14:40 GMT. Police say a lone attacker drove a car across Westminster Bridge, which sits adjacent to Parliament and is a heavily-used connection across the River Thames, killing at least two and injuring dozens of others as he plowed into a barrier on the north side of the embankment.

The attacker then lunged at an armed policeman outside the Houses of Parliament, stabbing him repeatedly before being shot by another officer on the scene. 

Police have issued no details with respect to the identity of the attacker, nor what motive he or she may have had, and have insisted that investigations are ongoing.

Prime Minister Theresa May, who had been in attendance at the Palace earlier Wednesday as part of her regular question-and-answer session with British lawmakers, has returned to her official residence at Downing Street and will chair a Cabinet Office Briefing Room, or COBRA meeting later this evening. COBRA meetings are called in response to civil emergencies, including terrorist attacks.

A medical professional working at St. Thomas' Hospital, which overlooks both the Houses of Parliament and Westminster Bridge, told TheStreet earlier Wednesday that at least six or seven people are likely to have been killed and that the Accident and Emergency department of the hospital has been placed on high alert and that hospital staff have been told not to leave the building.

London's Port Authority officials say that at least one woman was pulled from the Thames following the attack and is being treated by medical staff. 

The office of France's Prime Minister, Bernard Cazeneuve, has said that three French schoolchildren were among the injured in the busy tourist area of London that is frequently visited by large groups of students from around Europe.