Story highlights London's mayoral contest made international headlines as race and religion emerged as central issues

Khan's election makes him the first Muslim mayor of a Western capital city

Washington (CNN) Hillary Clinton congratulated the newly elected mayor of London, Sadiq Khan, in a tweet Saturday morning.

"Son of a Pakistani bus driver, champion of workers' rights and human rights, and now Mayor of London. Congrats, @SadiqKhan. --H" Clinton wrote.

Son of a Pakistani bus driver, champion of workers' rights and human rights, and now Mayor of London. Congrats, @SadiqKhan. -H — Hillary Clinton (@HillaryClinton) May 7, 2016

London's mayoral contest made international headlines as race and religion emerged as central issues, as Khan's election makes him the first Muslim mayor of a Western capital city. Clinton's tweet does not mention his religion.

Islamic extremism is a key issue in the 2016 presidential race, especially after Donald Trump, now the presumptive Republican nominee, proposed in December a temporary ban of all Muslims from entering the United States.

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