Republican Senator Lindsey Graham has died after brief and unexpected illness, US media reported.

Graham, one of President Donald Trump’s closest allies, died Saturday evening after a "brief and sudden illness,” his office said in a statement on social media. He was 71.

Graham had just returned from Kyiv, where he met Ukrainian President Volodymyr Zelensky on Friday. There were no known health concerns ahead of his trip.

The South Carolina politician was elected to the Senate in 2002.