Washington DC - Two senior Republican senators on Sunday urged President Donald Trump to reconsider his decision to revoke security protection for several top officials from his first administration, some of them highly critical of his policies.

Former Secretary of State Mike Pompeo and former National Security Advisor John Bolton are believed to be under threat from Iran for overseeing the 2020 US drone strike – ordered by Trump – that killed powerful Iranian general Qasem Soleimani.

And Anthony Fauci, who led the country's fight against Covid-19 starting in Trump's first term, has received death threats, including from some Trump supporters, over his handling of the pandemic.

Trump has defended the decision to revoke their security details, saying Friday they were not life-long privileges.

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But Tom Cotton, who chairs the Senate intelligence committee, and veteran Senator Lindsey Graham, a Trump confidant, urged the president to reconsider.

"I would encourage the president to revisit that decision for those being targeted by Iran," Cotton said on Fox News Sunday.

Officials might be wary of giving a president their unvarnished advice if they feared possible future reprisals from "China or the Mexican drug cartels," Cotton said.

Graham told CNN he agreed.

"Everybody doesn't deserve a detail all their life. It needs to be as needed. But...the threats seem to be real," Graham said on CNN's State of the Union.

When Trump was asked by a reporter whether he would feel any responsibility if anything happened to Fauci or Bolton, he replied: "No."

"They all made a lot of money," he said. "They can hire their own security."

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Bolton has become one of Trump's most outspoken critics since leaving the White House, while Pompeo briefly considered a Republican run for president, reportedly annoying Trump.

And the 84-year-old Fauci has become a hated figure for many on the right.

He told Politico last week that threats from extremists "create immeasurable and intolerable distress for me and my family."

The State Department has announced a $20 million reward in connection with an alleged Iranian plot to assassinate Bolton.

US officials have also accused Iran of seeking to assassinate Trump to avenge Soleimani's death.

Former US presidents receive lifelong Secret Service protection, unless they decline it.