US Secretary of State Rex Tillerson pressed NATO allies Friday to ramp up military spending and denounced Russia's "aggression" in Ukraine, toughening the Trump administration's tone toward Moscow.
Tillerson delivered the message as he met fellow NATO foreign ministers for the first time ahead of a May 25 summit to be attended by leaders including President Donald Trump.
"As President Trump has made clear, it is no longer sustainable for the US to maintain a disproportionate share of NATO's defence expenditures," Tillerson said in Brussels.
He urged his fellow foreign ministers to agree at the May summit to produce plans by the end of the year to meet the spending pledge.
NATO countries originally agreed at a summit in Wales in 2014 to contribute the equivalent of two percent of their gross domestic product to defence.
Seeking to draw a line under the funding row, NATO chief Jens Stoltenberg has sought to play down concerns that Trump is less committed to the 28-nation alliance than his predecessors.
"We see a strong US commitment to NATO, to the transatlantic bond not only in words but also in deeds," Stoltenberg said, citing increased US military deployments in eastern Europe.
Former Norwegian premier Stoltenberg said the European allies themselves realised the need to meet the citing conflicts to the east and south of its borders.
Tillerson's remarks were tougher than those previously made by Trump or his cabinet officials who have stressed better US relations with Moscow after they had sunk to a low under President Barack Obama over the crisis in Ukraine.
"We want to have a discussion around NATO's posture in Europe, most particularly in eastern Europe in response to Russia's aggression in Ukraine and elsewhere," Tillerson told reporters.
In his speech, Tillerson added that NATO was "fundamental to countering both non-violent, but at times violent, Russian agitation and Russian aggression."
US officials said Tillerson would work with NATO allies to press Russia to fulfil its obligations under the Minsk agreements to end the war in eastern Ukraine.
Russia in 2014 annexed Crimea from Ukraine and backed separatists in eastern Ukraine.
Allies have been alarmed at the prospect of Trump seeking to improve relations with Russia at the expense of support for the pro-Western government in Ukraine or NATO allies in former Soviet parts of eastern Europe.
Their concerns were reinforced when Tillerson initially planned to skip the NATO meeting, citing various commitments including a trip to Russia.
But Tillerson, a press-shy former oilman who had friendly ties with Russian President Vladimir Putin, agreed to attend when NATO rescheduled the meeting for Friday.
A senior NATO official told reporters Thursday on condition of anonymity that the Trump administration was now taking a more "mainstream" approach to the alliance and anxiety among allies had eased.
Tillerson arrived in Brussels following a visit to Turkey, a NATO ally and key player in both Syria and Iraq where Washington wants to defeat the Islamic State (IS) militant group.
In the last two years, IS has claimed or hailed a wave of deadly attacks in US and European cities, including Brussels.
But the funding row remains central.
NATO's 2016 annual report said only five countries met the two percent target -- the United States, Britain, Greece, Poland and Estonia -- while Washington still accounted for nearly 70 percent of combined alliance defence spending.
During a visit to NATO in February, US Secretary of Defense James Mattis voiced staunch support for NATO but warned that Washington could "moderate" its commitment if allies fail to pay up.
Trump said after a visit by German Chancellor Angela Merkel this month that Germany owes "vast sums of money" to NATO and the US.
But German Foreign Minister Sigmar Gabriel said it was "totally unrealistic" for his country to meet the two-percent target.
A NATO official told reporters however that Tillerson's funding demands were "well received" by the ministers, who told him what they were doing to meet their pledges.