By Warren Strobel and Lesley Wroughton

WASHINGTON (Reuters) - New U.S. President Donald Trump's "America First" rhetoric and confrontational negotiating style have sparked frantic calls to the White House and Congress from diplomats and lobbyists concerned the United States no longer has their back.

When word swirled through Washington on Thursday that Trump might be preparing to ease U.S. sanctions on Russia, worried European diplomats began calling the National Security Council and asking if the rumors were true, said a former U.S. official familiar with the situation.

The White House officials could not answer their questions because they, too, have been kept in the dark, said the former official, who requested anonymity because of the sensitivity of the matter.Trump's new United Nations ambassador, Nikki Haley, sent another shiver through America's allies on Friday, warning them that if they do not have Washington's back, she is "taking names" and will respond.

"Trump's foreign policy is totally unpredictable," said a senior official of the 28-nation European Union, which Trump has said is bound for a break-up.

Defense Secretary James Mattis and Secretary of State nominee Rex Tillerson "have said all the right things," the EU official said. "But this could be like the Iraq war policy all over again, when we saw how a segment of government decides policy, not the secretary of state."

Another Western diplomat said foreign ambassadors were explaining their countries' positions to Congress in the hope that they would find their way to the White House.

Other countries are expanding their lobbying efforts.

At the end of last year, Ukraine signed a $50,000-a-month lobbying contract with Haley Barbour, a former Republican chairman and Mississippi governor.

In January, the government-run China Council for the Promotion of International Trade hired Husch Blackwell LLP, to lobby about the importation of stainless steel, according to records filed with the Department of Justice.

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Some uncertainty is normal when a new U.S. president finds his footing and voice on foreign affairs and installs his people in policy-making slots.

But in the week since his inauguration, Trump has sent a blizzard of conflicting signals, and key slots at the State and Defense departments and the NSC remain vacant.

"We're trying to figure out who is who," one European diplomat said, referring to efforts to determine whether long-standing tenets of U.S. foreign policy still apply.

One of President Trump's first major meetings, with Mexican President Enrique Pena Nieto, was canceled due to Trump's demand Mexico pay for a border wall he plans to build. The two spoke by telephone on Friday after the cancellation.

Trump said Wednesday he would back safe zones for refugees in Syria, but gave no indication how he would coordinate this with Turkey, Russia and allies in Europe and the Middle East.

Presidential spokesman Sean Spicer's suggestion the United States would stop China from taking over territory in the South China Sea and Trump's Jan. 2 tweet that a threatened North Korean test of an intercontinental ballistic missile “won’t happen” could raise the chances of a military confrontation, Asian officials said.

Some commentators say it's too soon for allies to panic.

"It is not appropriate to be too worried, but it is not appropriate not to worry at all," said Fumiaki Kubo, a professor of American government history at the University of Tokyo.

A senior official from a member of the Five Eyes nations that make up the world's leading intelligence-sharing network said it was still important to keep intelligence channels open with Washington. The grouping comprises the United States, Australia, Canada, Britain and New Zealand.

"We will continue to share intelligence with the Americans, who supply the majority of information that circulates among the Five Eyes. If we hold data back from them, they could decide to do the same to us, and then we would suffer much worse consequences."

But others suggested that the greater the uncertainty and the longer it lasts, the greater the chances of miscalculations by other nations that could harm U.S. interests.

ASIAN NERVES

The high geopolitical anxiety is most evident in East Asia, where China's ambitions are colliding with longstanding U.S. dominance in the Pacific.

During his presidential campaign, Trump suggested Japan and South Korea, which rely on a U.S. security umbrella, should defend themselves or pay Washington more to do so.

Defense secretary Mattis will make his first overseas trip next week to the two countries, a choice intended to send a "reassurance message," a Trump administration official said.

"This is for all of the people who were concerned during the campaign that then-candidate, now President Trump was skeptical of our alliances and was somehow going to retreat from our traditional leadership role in the region," said the official, speaking on condition of anonymity.

Yet Mattis has voiced sharply different opinions from Trump on key questions, including the value of the NATO alliance and the threat from Russia, and that has led officials in Tokyo and Seoul to wonder who speaks for U.S. policy.

Trump took a call from President Tsai Ing-wen of Taiwan, which Beijing considers a rogue province, and has questioned Washington's decades-old adherence to the "one China" principle.

"China's attitude at the moment is very cautious, but that does not mean weak," said Shi Yinhong, who heads the Centre for American Studies at Beijing's Renmin University and has advised the government.

Allies, though, worry that instead of being based partly on shared values such as democracy, free trade, and the rule of law, their dealings with the United States might become transactional and start to resemble Trump's real estate deals."We are business people. We are not going to govern this country with diplomatic niceties; we are going to govern this country as a business," said a Western diplomat, quoting a Trump advisor.

(Additional reporting by Arshad Mohammed, Matt Spetalnick, Jonathan Landay, Ginger Gibson and David Brunnstrom in Washington, Robin Emmott in Brussels, Linda Sieg in Tokyo and Ben Blanchard in Beijing; Editing by John Walcott and James Dalgleish)