US President Donald Trump has said he had "very, very good discussions" with his Ukrainian counterpart Petro Poroshenko in Washington.
During the meeting, billed as a "drop-in", they discussed "support for the peaceful resolution to the conflict in eastern Ukraine", the White House said.
Ukraine has been fighting Russian-backed rebels in the east since 2014.
Mr Trump's previous calls for better US ties with Russia have worried Ukrainian authorities, observers say.
Tuesday's meeting came as Washington announced more sanctions relating to Russia's actions in Ukraine.
The measures target 38 organisations and individuals, including Russian government officials and also officials in Crimea - a Ukrainian region annexed by Russian three years ago.
Russian Foreign Minister Sergei Lavrov called the move "regrettable".
'A lot of progress made'
In a brief statement, the White House said the two leaders had also discussed "President Poroshenko's reform agenda and anticorruption efforts".
In televised comments, President Trump described Ukraine "a place that we've all been very much involved in and we've been seeing it and everybody has been reading about it".
He added that "a lot of progress has been made" between Ukraine and the US, without providing any further details.
Meanwhile, Mr Poroshenko said America was "one of the most reliable supporters" of Ukraine.
The "drop-in" meeting was described by a number of Russian analysts as a diplomatic snub for the Ukrainian leader.
But observers in Ukraine stressed on the importance of it coming before expected talks between Mr Trump and Russian President Vladimir Putin at a G20 gathering in Germany in July.
The US administration is facing claims of Russian meddling in the 2016 election and of possible links between the Trump campaign and the Kremlin.
Mr Trump has repeatedly denied the allegation, calling them a "witch hunt".
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In Washington, President Poroshenko also held talks with US Secretary of State Rex Tillerson and Defence Secretary Jim Mattis.
"The United States stands with you. We support you in the face of threats to sovereignty, to international law or to the international order," Mr Mattis said.