According to White House Press Secretary Sean Spicer, the US President was briefed on the situation and was continuing to monitor events.
The US State Department says it was also watching developments after the incident outside London's Parliament and urged Americans in London to avoid the area.
Spokesman Mark Toner said on Wednesday: “We stand ready to assist in any way the UK authorities would find helpful.”
He added that the US Embassy in London was closely following the news and stood ready to help any affected Americans.
According to the Associated Press, he said: “Our hearts go out to those affected.”
Mr Spicer said that Mr Trump has spoken with the British Prime Minister, Theresa May, after the incident. He did not immediately provide details of what was said.
He also said that Secretary of State Rex Tillerson, and Secretary of Homeland Security John Kelly, had issued statements and been inn touch with their British counterparts.
"I know the British government is investigating this now," he said. "We're going to monitor the situation. We're staying in touch with British officials."
Meanwhile, the New York Police Department has said it is increasing security at various locations across the city, including the British Consulate and Grand Central Station.
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