U.S. Secretary of State Rex Tillerson has arrived in Brussels to attend a March 31 NATO meeting that was rescheduled to allow him to attend.
A senior State Department official told reporters that Tillerson will push alliance members to increase their defense spending and will work with allies to press Russia to abide by the Minsk agreement to end the crisis in Ukraine.
The gathering is preparation for a May 25 NATO summit, which President Donald Trump has said he will attend.
Since his presidential campaign, Trump has pushed to get U.S. allies to increase their defense outlays to help ease the burden on Washington.
Trump's criticism of NATO -- calling it "obsolete" at one point -- and his long-stated desires to have closer relations with Russia have concerned many NATO allies.
NATO chief Jens Stoltenberg dismissed concerns that Trump is not as committed as his predecessors to the Western military alliance.
"They are very committed to NATO and the transatlantic bond because they see the importance of NATO for Europe, but they also see the importance of NATO for the U.S.," Stoltenberg reporters on March 30.
Some leaders are also concerned about Trump's commitment to end Russian interference in Ukraine.
Western nations have imposed sanctions against Moscow for its illegal annexation of Ukraine's Crimea region and for Russia's support of separatist fighters in eastern Ukraine.
The U.S. official said Tillerson will discuss ways of getting Russia to comply with the Minsk agreement, which set out steps to end the war between Kyiv and the separatists and restore Ukraine's control over its border with Russia.
Trump will also urge the allies to increase their role in fighting terrorism, the official said.
Tillerson initially planned to skip the NATO meeting, citing various commitments including a trip to Russia, forcing the allies to reschedule the event.