Donald Trump becomes US president

Donald Trump sworn in as 45th US president, in historic power transfer from President Obama.

In his inaugural address he vowed to fight for the "forgotten" Americans.

Taking aim at Washington elites, he vowed: "Our country will prosper again".

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UK Foreign Secretary Boris Johnson has congratulated President Donald Trump on taking office, saying Britain will work "hand and glove" with him for the "stability, prosperity and security of the world". 

"I want to offer my warmest congratulations to President Donald Trump on acceding to the most important political office in the world and I know that billions of people will be willing him to succeed in the months and years ahead, in the very great challenges that he faces," Johnson said.