U.K. Foreign Secretary Boris Johnson has refused to apologize for withering one-liners he's made about world leaders but he has won the support of Britain's closest ally as the country navigates its difficult path out of the European Union.

Johnson, who was hosting U.S. Secretary of State John Kerry in London on Tuesday, says people are "free to rake over" his past comments. But he says he's focused on dealing with the humanitarian crisis in Syria and the rise of the Islamic State group.

Later the two men will hold talks on Syria with European ministers and discuss the conflict in Yemen with foreign ministers from Saudi Arabia and the United Arab Emirates.

The 52-year-old Johnson once described Democratic front-runner Hillary Clinton as "a sadistic nurse in a mental hospital."