U.S. President Donald Trump took to Twitter amid the unfolding deadly drama in London on Saturday to offer U.S. help to Britain and to promote his controversial travel ban as an extra level of security for Americans.
British police rushed to two incidents in central London after a van plowed into pedestrians on London Bridge and reports emerged of multiple stabbings in the nearby Borough Market area.
Police said the attacks had been declared terrorist incidents.
At least six people were killed, police said.
"Whatever the United States can do to help out in London and the U.K., we will be there - WE ARE WITH YOU. GOD BLESS!" Trump said in one of two tweets.
Trump also spoke with British Prime Minister Theresa May to offer condolences and offered Washington's "full support" in investigating and bringing the perpetrators to justice, the White House said in a statement.
In another tweet, Trump said "We need to be smart, vigilant and tough. We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety!"
The U.S. Department of Homeland Security issued a statement late Saturday saying "At this time, we have no information to indicate a specific, credible terror threat in the United States."
Trump's appeal for his travel ban, which he says is needed to protect Americans from terrorist attacks, followed his emergency request that the Supreme Court reinstate the executive order that would bar people entering the United States from six predominantly Muslim countries.
Critics say his reasoning is flawed and assail the ban, which has been blocked by lower courts, as discriminatory.
The U.S. State Department condemned what it called "the cowardly attacks targeting innocent civilians" in a statement, and echoed Trump's readiness to provide any assistance that British authorities request.
"All Americans stand in solidarity with the people of the United Kingdom," State Department spokeswoman Heather Nauert said in the statement.
Trump was briefed earlier about the London Bridge incident by his national security team, according to White House spokesman Sean Spicer, who said on Twitter that security officials would continue providing the president with updates.
The State Department also said it was monitoring the situation and advised Americans in Britain to heed the advice of local authorities and maintain their security awareness.
"There is no credible threat or nexus to LA," the Los Angeles Police Department tweeted. "We ask Angelenos to stay vigilant."
The New York Police Department's Counterterrorism Bureau said on Twitter that its critical response teams had been deployed to heavily traveled pedestrian areas.
"Go about your Sat. night, NYPD cops are protecting you" the department's official account tweeted.
New York Gov. Andrew Cuomo said in a statement he had directed state law enforcement officials to step up security and patrols at high-profile locations, including airports, bridges, tunnels and mass transit systems.
Ariana Grande, the U.S. singer whose May 22 concert in Manchester, England was hit by a suicide bombing that killed 22 people and wounded 116, tweeted "Praying for London" after Saturday's attacks.