By Mark Hosenball, Arshad Mohammed and Matt Spetalnick

WASHINGTON (Reuters) - Foreign diplomats are expressing alarm to U.S. government officials about what they say are inflammatory and insulting public statements by Republican presidential front-runner Donald Trump, according to senior U.S. officials.

Officials from Europe, the Middle East, Latin America and Asia have complained in recent private conversations, mostly about the xenophobic nature of Trump's statements, said three U.S. officials, who all declined to be identified.

"As the (Trump) rhetoric has continued, and in some cases amped up, so, too, have concerns by certain leaders around the world," said one of the officials.

The three officials declined to disclose a full list of countries whose diplomats have complained, but two said they included at least India, South Korea, Japan and Mexico.

U.S. officials said it was highly unusual for foreign diplomats to express concern, even privately, about candidates in the midst of a presidential campaign. U.S. allies in particular usually don't want to be seen as meddling in domestic politics, mindful that they will have to work with whoever wins.

Senior leaders in several countries -- including Britain, Mexico, France, and Canada -- have already made public comments criticizing Trump's positions. German Economy Minister Sigmar Gabriel branded him a threat to peace and prosperity in an interview published on Sunday.

Trump's campaign did not respond to requests for comment on the private diplomatic complaints.

Japan's embassy declined to comment. The Indian and South Korean embassies did not respond to requests for comment.

A spokesperson for the Mexican government would not confirm any private complaints but noted that its top diplomat, Claudia Ruiz Massieu, said last week that Trump's policies and comments were "ignorant and racist" and that his plan to build a border wall to stop illegal immigration was "absurd."

The foreign officials have been particularly disturbed by the anti-immigrant and anti-Muslim themes that the billionaire real estate mogul has pushed, according to the U.S. officials.

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European and Middle Eastern government representatives have expressed dismay to U.S. officials about anti-Muslim declarations by Trump that they say are being used in recruiting pitches by the Islamic State and other violent jihadist groups.

On Dec. 7, Trump’s campaign issued a written statement saying that he was “calling for a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on.”

Trump subsequently said in television interviews that American Muslims traveling abroad would be allowed to return to the country, as would Muslim members of the U.S. military or Muslim athletes coming to compete in the United States.

There are also concerns abroad that the United States would become more insular under Trump, who has pledged to tear up international trade agreements and push allies to take a bigger role in tackling Middle East conflicts.

“European diplomats are constantly asking about Trump's rise with disbelief and, now, growing panic," said a senior NATO official, speaking on condition of anonymity.

"With the EU facing an existential crisis, there's more than the usual anxiety about the U.S. turning inward when Europe needs U.S. support more than ever."

Another of the senior U.S. officials said the complaints are coming mostly from mid-to-low ranking diplomats – described as “working level” - rather than from the most senior officials.

"The responses have ranged from amusement to befuddlement to curiosity," the official said. "In some cases, we've heard expressions of alarm, but those have been more in response to the anti-immigrant and anti-refugee sentiment as well as the general sense of xenophobia.”

More than a hundred Republican foreign policy veterans pledged this week to oppose Trump, saying in an open letter that his proposals would undermine U.S. security.

"A LOT OF QUESTIONS"

On Tuesday, General Philip Breedlove, the United States' top military commander in Europe, said that the U.S. elections were stirring concerns among America's allies.

“I get a lot of questions from our European counterparts on our election process this time in general," said Breedlove, who did not mention Trump by name. "And I think they see a very different sort of public discussion than they have in the past.”

While not confirming the content of private diplomatic contacts, some foreign officials acknowledged their governments' concerns about Trump.

A British official noted that in January, Prime Minister David Cameron said: "What Donald Trump says is, in my view, not only wrong, but actually it makes the work we need to do to confront and defeat the extremists more difficult."

A Chinese official referred to a statement last week from China's foreign ministry spokeswoman. Asked whether China was concerned about Trump's proposal to place high tariffs on Chinese goods, Hua Chunyin declined to comment on specific candidates. But she said "I want to stress" that China and the United States have "major responsibilities" in maintaining international political and economic stability.

Representatives of other countries publicly attacked by Trump, including Iran, Iraq, Saudi Arabia, Saudi Arabia, and Vietnam either had no comment or did not respond to requests for comments.

Several American foreign policy experts said foreign diplomats have complained to them as well.

"All foreign diplomats I’ve talked to are amazed at the Trump phenomenon and worried about it, especially in the Middle East and Europe,” said Elliott Abrams, senior fellow at the Council on Foreign Relations think tank who handled Middle East affairs at the National Security Council from 2001 to 2009 under then-President George W. Bush.

(Reporting by Mark Hosenball; additional reporting by Jonathan Landay, Phil Stewart, David Brunnstrom, and Emily Flitter; editing by Stuart Grudgings.)