"With respect to the release of information inappropriately…certainly, we condemn that," Tillerson told reporters. "We take full responsibility for that and we are — we obviously regret that that happened."
Manchester police stopped sharing intelligence with their US counterparts on Thursday after details about the attacker, the bomb and other aspects of the investigation were published by various media outlets.
On Thursday night, UK Counter-Terrorism Police chief Mark Rowley said information-sharing would resume after London got "fresh assurances" from Washington.
UK Prime Minister Theresa May had previously said she would address the issue with Trump.
Trump has ordered the Justice Department to investigate how the apparent leaks happened, and US Attorney General Jeff Sessions said Thursday that the probe had started.
Troubles with the assimilation of migrants lead these individuals to support acts of violence against compatriots as they do not feel part of a society, Tillerson added.
"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 neighbors. So I think it is extremely complex issue, this mass migration of people… is a problem for countries all over the world. It is one we have to learn better how to address," Tillerson told reporters at the joint press conference with UK Foreign Secretary Boris Johnson.
The US State Secretary snap visit to the United Kingdom had been announced on Thursday with the aim of expressing UK-US solidarity following the terrorist attack in Manchester.
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