WASHINGTON (BLOOMBERG) - US Secretary of State Rex Tillerson spent his first day on the job reassuring rattled US allies and his new employees that US foreign policy is in steady hands.

He then spent his first night watching as President Donald Trump's White House kept the world on its toes. By nightfall Thursday (Feb 2), news emerged of an imminent round of tougher sanctions on Iran, an unexpected statement cautioning Israel and a hasty effort to mend ties with Australia.

The start of Mr Tillerson's tenure as America's top diplomat was defined by the need to calm counterparts abroad whose faith in relations with the US has been shaken by Mr Trump's unpredictable and surprising approach to global affairs - including reported spats with Australian Prime Minister Malcolm Turnbull and Mexican President Enrique Pena Nieto.

"I suspect foreign leaders will be very eager to see him, so they have an outlet to express their concerns and also someone who might be able to explain some of the disturbing things they are seeing daily, and sometimes multiple times a day, out of the White House," said Mr Jon Finer, who was chief of staff under Mr Tillerson's predecessor John Kerry.

The next few weeks will reveal to what extent Mr Tillerson - accustomed to calling the shots as chief executive officer of Exxon Mobil Corp. - will have the power to temper Mr Trump's behaviour or pursue his own international diplomacy. Or whether he is relegated to delivering Mr Trump's latest views on foreign policy, no matter how much that antagonises US allies and adversaries.

"Rex Tillerson is a force of nature and he has a tremendous amount of organisational leadership experience and very strong views," said Dr Ariel Cohen, a senior fellow at the Atlantic Council in Washington. "However in the presidential republic that we are, the secretary of state serves at the pleasure of the president and implements policy that the president and the White House formulates."

Mr Trump's penchant for carving out an unpredictable foreign policy didn't pause for Mr Tillerson's first day. White House spokesman Sean Spicer issued a surprising statement on Israel on Thursday night, saying "the construction of new settlements or the expansion of existing settlements beyond their current borders may not be helpful" to reaching an Israeli-Palestinian peace agreement. Weeks earlier, Mr Trump had slammed a United Nations resolution criticising Israel's settlements policy.

'DEEP ADMIRATION' FOR AUSTRALIA

And after a tough phone call between Mr Trump and Australian Prime Minister Malcolm Turnbull, Australia's ambassador to the US had a more cordial meeting on Thursday with White House Chief of Staff Reince Priebus and senior counselor Stephen Bannon, who conveyed the president's "deep admiration" for the Australian people, according to a person familiar with the meeting.

In addition to talking with his counterparts in Mexico and Canada, Mr Tillerson spoke on Thursday with Israeli Prime Minister Benjamin Netanyahu and met with German Ambassador Sigmar Gabriel.

Mr Trump has frayed nerves of Nato allies in Europe over his comment that the alliance is obsolete, and in a recent interview, he faulted German Chancellor Angela Merkel, who he has repeatedly criticised for her policies welcoming refugees.

Mr Tillerson also sought to build a stronger relationship with State Department employees, many of whom are wary of the new administration after Mr Trump issued an executive order halting refugee inflows and barring entry to the US from seven Muslim-majority nations. On Tuesday, more than 900 diplomats and staff in the department signed a memo to Mr Tillerson opposing Mr Trump's immigration order, saying it was contrary to American values.

In a speech to several hundred staff at the agency's headquarters, Mr Tillerson struck an amiable, sometimes jokey tone. He promised to defer to their experience, referred to himself as the "new guy," and asked that staff treat one another with respect, saying "before we are employees of the State Department, we are human beings first."

"I will depend on the expertise of this institution," he said. "You have acute knowledge and experience that cannot be replaced anywhere else."

WALL OF HONOUR

After his remarks, which didn't touch on foreign policy, Mr Tillerson and his wife Renda stopped to pay their respects at a wall engraved with the names of diplomats who died on duty. He bowed his head, ran his fingers over a few names, and then walked slowly through the crowd, shaking hands with staff.

Now, Mr Tillerson's success will hinge on how strong a relationship he can forge with Mr Trump and whether foreign leaders will trust that he speaks for the president.

Mr Trump has said he hired Mr Tillerson precisely because of the relationships he cultivated with world leaders during his 41-year career at Exxon. In a speech on Thursday at the annual National Prayer Breakfast, Mr Trump said Mr Tillerson was "going to go down as one of our great, great secretaries."

"The key will be whether Tillerson is able to establish - in some notable way - his authority," said Mr Dennis Ross, who served as a foreign policy adviser to three US presidents. "Can he give a speech that seems to define the approach to foreign policy that is not contradicted? Do his pronouncements get reinforced, not undercut? Are there policy areas where he seems to be given the lead?"