Security has been beefed up in Los Angeles as a "precaution" in the wake of the Westminster terror attack which left four dead, the city's mayor has said.
Eric Garcetti said he would offer assistance to his London counterpart Sadiq Khan and described the incident as "an attack on the idea of freedom".
He told the Press Association: "It's unfortunately the times we live in that this can strike anywhere.
"In fact it's the freer places, like the United States, like Paris, like London, where the attacks are made.
"It's not just an attack on people, it's an attack on the idea of freedom.
"My wife and I met in the UK, I lived there for four and a half years. I lived in London so personally my heart broke to see what was happening.
"Los Angeles stands with London, one of the great cities in the world."
Mr Garcetti said a decision had been taken to "beef up security in key infrastructure" in Los Angeles, including the city's airport.
"We know of no connection of any threat here, but just as a precaution," he added.
President Donald Trump has offered the "full co-operation and support" of the United States in responding to the Westminster terror attack and "bringing those responsible to justice".
He had earlier described the incident outside the Houses of Parliament as "big news".
A White House spokesman said: "President Donald J. Trump spoke today with Prime Minister Theresa May of the United Kingdom to offer his condolences on today's terror attack in London and his praise for the effective response of security forces and first responders.
"He pledged the full co-operation and support of the United States government in responding to the attack and bringing those responsible to justice."