London - US Secretary of State Rex Tillerson insisted extremists must be wiped out and that "fires for justice" were burning hot over the Manchester attack, during a solidarity visit to Britain on Friday.
Tillerson joined his British counterpart Boris Johnson at the foreign secretary's official residence in London to write a message in the book of condolence for victims of Monday's suicide bombing, which killed 22 people.
Tillerson wrote that the attack broke people's hearts all across the United States.
Britain was renowned for its "strength in times of darkness" and would not be broken by terror, he told reporters after 90-minute talks with Johnson.
"Even as our ally and friend mourns, the fires for justice burn very hot in all of our hearts," Tillerson added.
"We will drive out the terrorists and the extremists... we must drive them off the face of the Earth."
Priests, rabbis and "every imam in every mosque must condemn the souls of those who carried out these attacks".
Tillerson's first official visit to the UK was a previously unscheduled stop on his return to the United States from Thursday's NATO summit in Brussels.
The Manchester attack was perpetrated by Salman Abedi, a 22-year-old born and brought up in a Libyan family in the city he targeted.
Both secretaries acknowledged there were problems in properly integrating immigrant communities.
Tillerson said Western countries had to address their "inability to assimilate people", while Johnson said immigrants "have to become British".
"We seem to have difficulty assimilating those people so that they feel part of our society and would never consider supporting acts of violence against their fellow citizens and their fellow neighbours," Tillerson explained.
Johnson said Britain should aspire to achieve integration.
"But I'm not going to pretend to you that every individual and every community feels as well-adjusted as they should," the former London mayor said.
"When people come to this country, they have to become British. And if they're going to live here and work here, they must become part of our society and espouse its values."
British investigators have shared information on the Manchester attack with their closest defence ally, but repeated leaks of the material out of Washington have infuriated London.
Tillerson tried to provide reassurance during his visit.
He said the United States took "full responsibility" for the leak of pictures and details shared by the British investigators.
"We condemn that," he said.
"We take full responsibility for that and we obviously regret that that happened."
The "special relationship" between London and Washington "will certainly withstand this particular unfortunate event", Tillerson added.