Washington (AFP) - A global firestorm erupted Tuesday over Donald Trump's call to bar Muslims from entering the United States, as the White House branded him a "carnival barker" unfit to lead and his campaign rivals rounded on him.

Trump, the leading candidate for the Republican presidential nomination, made the provocative remarks -- just his latest on a range of topics on the campaign trail -- after last week's shooting that left 14 dead in California by a Muslim couple said to have been radicalized.

In a rare primetime speech to the nation from the Oval Office on Sunday, President Barack Obama called the attack in San Bernardino an "act of terrorism," but stressed that it was not "a war between America and Islam."

Less than 24 hours later, Trump's bombastic bid for the White House plumbed what critics called new depths and triggered calls for him to be barred from taking power after he urged a "total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on."

The 69-year-old billionaire real estate mogul was unrepentant Tuesday, even as criticism rained down from the White House and as far afield as London and Cairo, where Egypt's official religious body Dar al-Iftaa denounced his comments as "extremist and racist."

The strongest reaction came in the United States, where White House spokesman Josh Earnest said Trump's proposals were unconstitutional and challenged the mogul's fellow Republicans to denounce him.

Earnest was scathing and deeply personal, painting Trump -- who has never held elected office -- as a "carnival barker" with "fake hair."

"What Donald Trump said yesterday disqualifies him from serving as president," concluded Earnest, describing the remarks as "offensive" and "toxic."

Trump, whose comments were extreme even by his populist standards, was similarly lambasted by leading Republicans and campaign rivals.

Trump was the "ISIL man of the year," thundered US senator and fellow presidential candidate Lindsey Graham, referring to his belief that Trump was succeeding only in fueling the radical ideology of the Islamic State group.

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"Do you know how you win this war? You side with people in the faith who reject this ideology, which is 99 percent," Graham told CNN, before invoking Trump's campaign slogan -- "make America great again."

"And do you know how you make America great again?" asked Graham, who is lagging badly in the nomination race.

"Tell Donald Trump to go to hell."

Other Republican contenders including Marco Rubio, John Kasich, Chris Christie and Jeb Bush, as well as Republican House Speaker Paul Ryan, also swiftly rejected Trump's proposal.

Hillary Clinton, the Democratic presidential frontrunner, said Trump was playing "right into the hands of terrorists" and Rick Kriseman, the Democratic mayor of Saint Petersburg, Florida, tweeted: "I am hereby barring Donald Trump from entering St. Petersburg until we fully understand the dangerous threat posed by all Trumps."

- 'Complete distortion' -

Muslim leaders in the United States also hit out.

Sohaib Sultan, Muslim Life Coordinator and Chaplain at Princeton University, drew parallels between Trump and the radical ideology of the Islamic State group.

"ISIS is to Islam what Donald Trump is to American values: a complete distortion of everything that we as a country and a society stand for."

But Sultan also lambasted other Republicans.

"I know a lot of Republican candidates are jumping on Trump about his latest comments, but a lot of Republican candidates have really been using similar type of rhetoric throughout the election cycle as well," he told CNN.

Trump showed little inclination to back down, however, and instead compared the proposed ban to actions taken by Franklin D. Roosevelt against Japanese and German "enemy aliens" during World War II, though he stopped short of advocating internment camps.

Asked in an interview on MSNBC's "Morning Joe" program if his proposal went against treasured American values, he responded: "No, because FDR did it!"

But that failed to quell the firestorm, with "Harry Potter" author J.K. Rowling saying he was worse than the notorious villain in her blockbuster books.

"How horrible. Voldemort was nowhere near as bad," she tweeted -- a theme quickly picked up by thousands of other Twitter users.

The British government was similarly unimpressed.

Prime Minister David Cameron "completely disagrees" with the remarks, which are "divisive, unhelpful and quite simply wrong," a spokeswoman for the Conservative leader said.

In Geneva, the United Nations refugee agency -- though not directly responding to Trump's remarks -- warned that rhetoric in the US presidential campaign was threatening a key refugee resettlement program in the United States.