Rex Tillerson's sudden departure from the White House severs a vital cord between Britain and the United States as Prime Minister Theresa May grapples with her country's pending exit from the European Union and a potentially dangerous standoff with Russia following the attempted murder of a former spy living in the United Kingdom.

Tillerson, who was fired by President Donald Trump as U.S. Secretary of State Tuesday, was seen as a reliable ally for May inside the White House and a consistent supporter of Britain's broader post-Brexit ambitions. Tillerson was also the most prominent U.S. official to publicly support Britain's allegation that Russia was behind the suspected poisoning of former intelligence agent Sergei Skripal and his daughter, Yulia, last week in the southeastern city of Salisbury.

"It appears that it clearly came from Russia, whether it came from Russia with the Russian government's knowledge is not know to me at this point," Tillerson said Monday. "We agree that those responsible - both those who committed the crime and those who ordered it - must face appropriately serious consequences."

His comments followed May's assertion to Parliament Monday that "should there be no credible response" from Moscow, "we will conclude that this action amounts to an unlawful use of force by the Russia state against the United Kingdom."

Tillerson's views, however, were not fully-endorsed by the broader Trump administration, suggesting he was either out-of-step with his boss or speaking on behalf of the U.S. government.

"It sounds to me like they (Britain) think it was Russia, and if we agree with that, we will take action," is all Trump would say when pressed by reporters Tuesday in Washington.

Either way, his support for May's attempt to isolate Russia on the Skripal affair -- the second murder of a former Russian intelligence official on British soil in the past 12 years -- was seen as significant for a Prime Minister struggling to express the value of the so-called "special relationship" that exists between Britain and the United States.

Watch: President Trump Replaces Rex Tillerson With CIA Director Mike Pompeo

That relationship, May and her Brexit-supporting allies have argued, will allow Britain to cut favorable trade deals with the world's biggest economy when it leaves the EU in March of next year. However, Trump's decision to slap steep tariffs on steel and aluminium imports, as well as his reluctance to confront what many see as Russian political aggression in Europe and the Gulf, has left May with few allies on the world stage and weakened her position at home.

The news of Tillerson's sacking, as well as further evidence that consumer price inflation in the United States remains relatively muted, helped push the U.S. dollar sharply lower against a host of major currencies, including the pound, which rose 0.35% to 1.3954.

However, Britain's modest near-term growth prospects (the OECD said earlier today that the U.K. economy will have the slowest rate of advance in the G20 over the next two years), its pending exit from the European Union and its sudden loss of a key ally in Washington, the currency's recent volatility in unlikely to ease.