Republican Senator Lindsey Graham, a close ally of US President Donald Trump, has died at the age of 71.

His office released a statement saying he died on Saturday evening following "a brief and sudden illness".

Elected to the Senate in 2002, the South Carolina politician was one of Washington's most influential voices on foreign policy.

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

In a social media post marking the senator's death, Trump said Graham was a "true American Patriot".

While Trump and many of his allies have been lukewarm in their support for Ukraine and have taken a more conciliatory tone towards Russia, Graham was a staunch supporter of arming Kyiv and applying sanctions against Moscow.

In his most recent trip to the country, Graham was working on a version of the Russia sanctions bill, which he said would give "tools to President Trump to end this war".

Zelensky said he was "deeply saddened" by the news of the senator's death.

In a post on his official X account, he said Graham had visited the country 10 times since Russia's full-scale invasion and was "with our people when it was most needed".

"America and the world have lost a determined leader," he added.

Graham initially clashed with the US president.

He told CNN in 2015 that Trump was "a race-baiting, xenophobic, religious bigot", and during the 2016 campaign he posted on social media: "If we nominate Trump, we will get destroyed… and we will deserve it."

After the US Capitol riots in 2021, Graham gave a speech on the Senate floor in which he said: "Trump and I, we've had a hell of a journey. I hate it to end this way.

"All I can say is a count me out. Enough is enough."

But he later became one of his staunchest backers. He voted against convicting Trump in the 2021 impeachment trial, and supported Trump in the 2024 election.

He told the BBC in 2023: "There is a dark side to Donald Trump… and he was a very good president. But I am sticking with him because I saw what he did." He cited Trump's record on the US southern border, the killing of Iran's powerful military commander Qasem Soleimani and the appointment of conservative judges.

Graham was known for his interventionist stance in foreign policy, with his website stating that Graham "consistently pushed for outcomes in the War on Terror that protect our long-term national security interests".

He voted in favour of military action against Iraq in the wake of the September 11 attacks in 2001 and was opposed to the withdrawal of US troops from Afghanistan in 2021, describing it as a "sad and dangerous event for US national security".

"Jihadists all over the world are celebrating," he added. "America will be seen as weak."

Graham was a staunch supporter of Israel.

Israel's Prime Minister Benjamin Netanyahu paid tribute to Graham on Sunday, saying "Lindsey understood that the security of Israel and America are inseparable".

Israel lost "one of its greatest friends", he added.