President Donald Trump is due to sign off on a new security arrangement with Denmark and Greenland, as well as meet leaders from Ukraine and Persian Gulf nations.

"The pain of fraternal grief can cloud reason," Buckingham Palace said in response to claims made by Princess Diana's brother in a new book.

The men are accused of being members of an organized criminal network that defrauded women out of more than $6 million through online relationships, South African police said.

The Trump administration said it would modify the scope of existing tariffs and introduce new bans on Canadian products in the latest escalation of the trade war.