US president Donald Trump has described the London Bridge terror attack as "horrific" and vowed that "this bloodshed must end".
Mr Trump's remarks, made during a Sunday night fund-raising event at Ford's Theatre in Washington DC, were his first public comments on the atrocity in which seven people died.
Up to now, the president had expressed his views only on Twitter.
Earlier, Mr Trump criticised London's mayor Sadiq Khan after he sought to reassure people about a stepped-up police presence on city streets.
In a series of tweets, President Trump challenged Mr Khan for saying there was "no reason to be alarmed".
Mr Trump also repeated calls for his stalled travel ban, took on gun control supporters and pledged that the United States would be there to help London.
At the fund-raiser Mr Trump said he would do whatever was necessary to protect the United States from a "vile enemy" that had waged war on innocents for too long.
"This bloodshed must end, this bloodshed will end," he said, with his wife Melania beside him.
Mr Trump made his comments at the conclusion of the event for Ford's Theatre - the scene of one of the most famous acts of bloodshed in American history: the assassination of Abraham Lincoln.
"America sends our thoughts and prayers and our deepest sympathies to the victims of this evil slaughter and we renew our resolve, stronger than ever before, to protect the United States and its allies from a vile enemy that has waged war on innocent life, and it's gone on too long," Mr Trump said.
"As president, I will do what is necessary to prevent this threat from spreading to our shores and work every single day to protect the safety and security of our country, our communities and our people."
Across the world in Sydney, Australia, US defence secretary Jim Mattis and secretary of state Rex Tillerson pledged unity with America's longtime ally in fighting Islamic extremists who seek to intimidate the West.
"We are united, as I said, in our resolve, even against an enemy that thinks by hurting us they can scare us," Mr Mattis said.
"Well, we don't scare."
In their first joint appearance abroad, Mr Mattis and Mr Tillerson spoke alongside their Australian counterparts at the opening of a joint meeting expected to touch on a range of subjects including defeating the Islamic State group, stabilising Afghanistan and dealing with North Korea's nuclear threats.
Mr Tillerson said the enduring US-Australian alliance would prevail in "this common fight we share against the most heinous of actions we've seen most recently in London yet again".
In the London attack, three men drove a van over London Bridge on Saturday and struck pedestrians before crashing the vehicle outside a pub.
The attackers, wielding blades and knives, ran to nearby Borough Market and stabbed people in several different restaurants.
Seven people were killed and at least 48 were taken to hospital.
Police fired 50 bullets to stop the violence, killing the three attackers and wounding one member of the public.
In her opening remarks, Australian foreign minister Julie Bishop said "countering terrorism" would be high on the meeting's agenda.
"The global terrorist threat is ever evolving, we've seen brutal attacks in a number of European cities, we've thwarted attacks here in Australia, and so we want to discuss with you, the links back into the Middle East, the role we're playing with you in Iraq and Syria and also Afghanistan," she said.
"We are united in our resolve to defeat Isis, the Islamic State terrorist organisation and its ilk."
Australian defence minister Marise Payne said her government was concerned by IS links in Asia and the Pacific.
"For Australia, from our perspective today it's important that we do discuss Isis' links in south-east Asia, violent extremist organisations and the risk that returning foreign fighters who may endeavour to resume positions in their own countries might pose in this region," she said.
"They'll come back with battlefield skills, they'll come back with hardened ideology, they'll come back angry, frustrated, and we need to be very aware of that."