U.S. officials took immediate protective steps against a new terrorist attack Tuesday in the hours after three deadly explosions rocked the airport and a subway station in Brussels.
The U.S. embassy in Brussels recommended that Americans stay where they are and avoid public transportation in the Belgian capital. It said U.S. citizens there should monitor media reports, follow instructions from authorities and "take the appropriate steps to bolster your personal security."
The U.S. Homeland Security agency said it is closely monitoring developments in the Brussels attacks and said it "will not hesitate to adjust our security posture, as appropriate, to protect the American people." It urged the public to immediately report any suspicious activity to local authorities wherever they are.
One senior U.S. intelligence official said, "The intelligence community continues to assess the situation in Brussels and is staying in close contact with our Belgian and European partners."
President Barack Obama, on the third day of a visit to Cuba, was briefed on the Brussels attacks.
New York, Washington
New York and Washington authorities boosted security patrols in the wake of the attacks.
New York police said there was no indication the Brussels explosions were related to the biggest U.S. city, but said officers had been dispatched to crowded areas and transit locations "out of an abundance of caution to provide police presence and public reassurance."
In Washington, the regional subway system sent officers with bomb-sniffing dogs into train stations for security checks, although it too said the patrols were precautionary and that there were no known credible threats against the national capital.
National Security correspondent Jeff Seldin contributed to this report