A vehicle speeding toward a U.S.-Canada bridge from the American side crashed and exploded at a checkpoint in Niagara Falls on Wednesday, killing two people and prompting the closing of border crossings in the area, authorities said. New York Gov. Kathy Hochul said there was “no indication of a terrorist attack.”

Much remained unclear about the crash, which investigators were working to understand. Hochul said it wasn’t clear whether the driver was intentionally heading for the Rainbow Bridge across the Niagara River when the vehicle hit a median and flew into the air.

“Based on what we know at this moment,” she said, “there is no sign of terrorist activity in this crash.”

It prompted the closing of four border crossings and raised concerns on both sides of the border. The White House said President Joe Biden was “closely following developments,” and Canadian Prime Minister Justin Trudeau said officials were “taking this extraordinarily seriously.”

“This is obviously a very serious situation in Niagara Falls,” Trudeau said in Parliament before excusing himself from Question Period in the House of Commons to be briefed further.

The two deceased people were in the vehicle, a law enforcement official told The Associated Press. The official was not authorized to discuss details of the investigation publicly and spoke on condition of anonymity.