Veteran US Senator John McCain diagnosed with brain cancer

Veteran US Senator John McCain has been diagnosed with brain cancer his office announced.

His office issued a statement saying that McCain has been treated at Mayo Clinic and his family are reviewing treatment options.

"The senator's doctors say he is recovering from his surgery 'amazingly well' and his underlying health is excellent," the statement read.

His office said that the 80-year-old former war veteran had received an "outpouring of support" and is in good spirits.

Doctors at Mayo clinic said that the senator went to surgery to remove a blood clot from above his left eye last week.

"[Tests] revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot," the Mayo Clinic, whose doctors performed the surgery in Phoenix.

He remove a blood clot from above his left eye last week and tests.

Glioblastoma is a particularly aggressive brain tumour affecting adults. It is of the same category of cancer that led to the death of another icon of the US Senate, Ted Kennedy, who died in 2009 at age 77.

McCain has had several malignant melanomas removed in the past three decades.

Experts had said this week that McCain's latest operation suggested the possibility of a return of cancer, AFP reported. 

McCain has cut a controversial figure in US politics, but his policies and principles have seen him win support on both sides of the house.

Often described as a hawk, McCain has been a strong opponent of Russian expansionism in Europe and been critical of fellow Republican leader President Donald Trump's relationship with Moscow.

He has also been a vocal critic of Syrian President Bashar al-Assad and called for US intervention to stop the regime's horrific bombing of opposition areas.

McCain has also been strongly opposed to torture, including water boarding, which has been used by the CIA and called for Guantanamo Bay to be closed.

Despite their differences, Trump also gave his heartfelt support for McCain.

"Senator John McCain has always been a fighter. Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family," President Donald Trump said in a statement. "Get well soon."

Trump has previously faced criticism for mocking McCain for being captured during the Vietnam War after his plane was shot down during a bombing mission.

"I like people who weren't captured," Trump said.

Trump was repeatedly tortured by Vietnamese captors during his years in captivity.

McCain has, however, backed Trump's campaign to repeal and replace Obamacare, which would see millions of Americans without medical insurance.

Former President Barack Obama also hailed the Republican senator.

"John McCain is an American hero & one of the bravest fighters I've ever known," Obama said on Twitter. "Cancer doesn't know what it's up against. Give it hell, John."

Agencies contributed to this story.