The explosion that occurred earlier today on the Rainbow Bridge in Niagara Falls, which connects the United States to Canada, was likely caused by a careless driver, according to initial estimates, sources familiar with the matter told Reuters.

The FBI seriously considered the possibility as an attempted terrorist attack and for this reason government buildings were evacuated and the border crossings between the US and Canada were closed.

A spokesman for the local mayor said the Rainbow Bridge would remain closed until further notice and that federal agencies were investigating the case.

Footage from the scene shows smoke and damage to the checkpoint that drivers pass through when entering the US, at least one fire engine and several police cars. Local station WKBW TV reported that an explosion may have occurred.

Another local station, WIVB, reported that all four US-Canada border crossings in western New York had been closed, but Reuters was unable to verify that information.

New York State Governor Kathy Hokul said in a post on Platform X that she was “aware of the incident” and is monitoring the situation. “State agencies are on the ground, ready to provide assistance,” he added.

The White House is closely monitoring the situation at the Niagara Falls border crossing on the US-Canada border, a US administration official said.

Canadian Prime Minister Justin Trudeau was also informed of the incident. The country’s Ministry of Public Security said the government was taking the incident “very seriously”, but it was still “too early” to say whether it was a deliberate act.

Public Security Minister Dominique LeBlanc said all border security measures had been stepped up and that he would soon speak with his American counterpart, Homeland Security Secretary Alejandro Mayorkas.