London is one of the visited cities in the worlds.

But now, London's massive tourism sector could come under pressure following a deadly terrorist attack in the heart of the city.

A lone attacker used a vehicle to run down pedestrians Wednesday on Westminster Bridge before fatally stabbing a police officer on the grounds of the U.K. Parliament.

Three people were killed in the attack and scores were injured. The suspect was also killed. ISIS claimed responsibility for the attack, but the group offered no proof of its involvement.

The incident occurred in a key destination for tourists in central London, where visitors often gather to take pictures of Big Ben and the Houses of Parliament. Some of the injured victims were visiting from countries including France, Australia and China.

The attack could have a major impact on London's booming tourism industry - especially in the busy summer months to come. The capital city welcomes up to 20 million visitors per year, making it among the top three most visited destinations in the world.

Some travelers may now choose to wait before booking flights to London. Other tourists may cancel their trips or avoid the city altogether.

London tourist spending has grown rapidly over the past year, increasing by more than 7% to nearly $20 billion in 2016.

The industry has benefited from a sharp drop in the value of the U.K. pound following the June Brexit referendum. That's made visits much cheaper for foreign visitors. Tourism directly supports roughly 500,000 jobs in the capital, according to U.K. Tourism Alliance.

London officials will be hoping to avoid a hit to tourism similar to the one suffered by Paris in the wake of a series of high-profile terrorist attacks.

France as a whole experienced a 7.3% drop in tourism spending in 2016, according to the World Travel & Tourism Council. The Louvre museum has seen attendance fall by 21% over the past two years.