The White House said Monday that President Donald Trump still intends an early exit for U.S. troops in Syria, as French President Emmanuel Macron attempted to walk back his suggestion that he had convinced Trump to keep them there for the "long term."

Macron's remarks on Sunday had hinted at a major policy shift for Trump, who had said he wanted a U.S. departure from Syria "very soon." But "our policy hasn't changed," White House spokeswoman Sarah Huckabee Sanders said, and Trump remains focused on defeating the Islamic State and on getting countries in the Persian Gulf to pick up the financial and military burden of Syria stabilization in the future.

The United States, France and Britain have all offered official justifications for their joint military strike on Syrian chemical weapons sites last weekend, as well as their own version of what it means for Syria's civil war.

In London, British Prime Minister Theresa May rejected political criticism that she acted on Trump's "whims" and said that her decision to send Royal Air Force warplanes to attack Syrian targets was not done as a favor to the U.S. president.

"We have not done this because President Trump asked us to do so," May told the House of Commons on Monday. "We have done it because it is in our national interest to do so."

Averting an "overwhelming humanitarian catastrophe is permissible under international law," May said.

Macron and Trump also have cited the preservation of international law against the use of chemical weapons, although Trump has said his constitutional powers to protect "U.S. interests" provided authority to order the strikes without congressional consultation.

Russia, Syrian President Bashar al-Assad's main backer, has said that an alleged chemical attack on April 7 in the Damascus suburb of Douma did not happen, and that it was a provocation staged by anti-Assad rebels.

May said British confidence that the Syian government was responsible for the chemical attack, which killed dozens of civilians, was based on "a significant body of information - including intelligence." U.S. Defense Secretary Jim Mattis also alluded to unspecified "intelligence" that reached him last Friday and convinced him that the Syrian government was indisputably responsible for the attack.

In both cases, the reference was based on electronic intercepts acquired by France and passed on to the United States and Britain, U.S. officials said. U.S. intelligence agencies declined to comment on the reported intercepts.

Although the administration has said its twofold strategy in Syria is to defeat the Islamic State and create conditions for a political settlement of Syria's civil war, it has also said its own direct involvement only concerns the former.

On Sunday, Macron said that despite Trump's pledge to disengage from Syria, "we convinced him that it was necessary to stay there long-term." That brought a quick denial from the White House and a Monday attempt by Macron to at least partially backtrack.

Speaking at a news conference during a visit to New Zealand, Macron said defeating the militants remains the military objective for France and the United States, and that the mission would end on "the day" that is accomplished.

"I did not say" that either country "would remain militarily engaged in Syria in the long term," he said.

But Macron added that "I'm right to say that the United States of America - because it decided to carry out this intervention with us - fully realized that our responsibility went beyond the war on Daesh," the Arabic term for the Islamic State, "and that we also have a humanitarian responsibility on the ground and a long-term responsibility to build peace."

Trump remains unpopular in Britain and France. Both Macron and May are anxious not to appear subservient to the president, even as they try to convince him of the value of their alliance.

That value, they hope, will pay dividends next month, when Trump must decide whether to drop out of the Iran nuclear deal to which all of them - along with Germany, Russia and China - are signatories.