US Secretary of State Rex Tillerson will miss a meeting of Nato foreign ministers next month, US officials say.
He will instead travel to a G7 meeting in Sicily, Italy, and then to Moscow to meet Russian leaders.
Under Secretary of State Tom Shannon will represent the US at the Western military alliance meeting in Brussels.
The US State Department said that when it realised Mr Tillerson would be absent for the 5-6 April meeting, it offered alternative dates to Nato.
Spokesman Mark Toner said the United States remained “100%” committed to the security alliance.
During his election campaign, Mr Trump expressed admiration for Russian President Vladimir Putin and described Nato as “obsolete”.
A negative narrative – Barbara Plett Usher, BBC State Department correspondent
It’s not unprecedented for a US secretary of state to skip a Nato meeting, but it is rare. The last time was when Colin Powell had to cancel during the 2003 Iraq War.
So the decision to do so reopens questions amongst European governments already anxious about Donald Trump’s commitment to the alliance. Publicly the State Department cites only scheduling difficulties, but the Nato meeting coincides with a visit to the US by the Chinese President Xi Jinping. And Rex Tillerson laid the groundwork for that on a recent trip to Asia at a time when the threat from North Korea has forced itself to the top of the administration’s agenda.
In recent weeks, US cabinet ministers and even Mr Trump have also reassured Nato allies about Washington’s continued support (while deploying thousands of troops to bolster central and eastern Europe against any threat of Russian interference).
But the president’s criticisms have continued. And Mr Tillerson’s plan to meet leaders of a more assertive Russia later in April before meeting Nato allies also feeds a negative narrative rather than one of reassurance. Given the State Department is now suggesting alternative dates to Nato, perhaps Mr Tillerson’s got the message.
Mr Tillerson had close links with the Russian government while he was CEO of Exxon Mobil and has questioned the sanctions imposed on Russia after its annexation of the Crimea region.
During a visit to Nato headquarters in Brussels last month, US Vice-President Mike Pence attempted to reassure US allies about the new government’s commitment to them.
But he also said that Mr Trump expected Nato members to make substantial progress by the end of the year towards meeting agreed defence spending increases.
Mr Tillerson will meet Nato diplomats this week in Washington for a conference on defeating the Islamic State group.