New York police strengthened security across British sites in New Yolk  on Wednesday after an assailant stabbed a policeman outside Britain’s parliament in Westminster and was later shot by police, Police Department  said.

“Heavily armed officers and explosives-detecting dogs were deployed to the locations, including the British Consulate and the British Mission to the UN in Manhattan.

“You will see a larger presence of the dogs at these locations, as well as (officers) armed with the long guns”, James Waters, " the Police Department’s Counterterrorism Chief, said.

Four people died and at least 20 were injured in what British police called a “terrorist incident” that also unfolded on nearby Westminster Bridge where witnesses said a car crashed into pedestrians.

“New York police previously boosted security at prominent sites around the city after large-scale attacks in Paris, Brussels and San Bernardino, California, out of an abundance of caution.

“Police are concerned about copycat assailants, but there was no specific threat to New York City on Wednesday’’, Police Commissioner James O’Neill said.

Separately, the U.S. Department of Homeland Security said it would lend support to Britain’s investigation of the attack, but that the U.S. security posture was unchanged.

“We are in close contact with our British counterparts to monitor the tragic events and to support the ongoing investigation”, the department said in a statement.