U.S. Vice President Mike Pence, Defense Secretary Jim Mattis, and Homeland Security Secretary John Kelly are leading the U.S. delegation to the February 17-19 conference, known for providing an open and informal platform for allies -- and adversaries -- to meet directly.
Petro Poroshenko will meet with Pence, the Ukrainian president's website said. Meanwhile, a senior U.S. administration official told CNN that Pence will also meet with German Chancellor Angela Merkel.
The conference is taking place amid concerns over the Trump administration's commitment to NATO and posture toward Russia.
Merkel, UN Secretary-General Antonio Guterres, European Council President Donald Tusk, and NATO Secretary-General Jens Stoltenberg are among the group of more than 30 heads of state and government, 80 foreign and defense ministers, and other officials expected to attend.
Trump triggered considerable alarm last month by calling NATO 'obsolete,' though he has subsequently told European leaders he agrees on the 'fundamental importance' of the military alliance.
He has emphasized the need for all members to pay a fair share for defense, an issue that NATO leaders themselves have pushed for years.
Mattis told the alliance's 27 other defense ministers in Brussels on February 15 that Trump had 'strong support for NATO' and assured Stoltenberg that 'the alliance remains a fundamental bedrock for the United States.'
However, Mattis also told fellow NATO members they needed to increase their military spending by year's end or risk seeing the United States curtail its defense support.
Conference organizer Wolfgang Ischinger, a former German ambassador to the United States, said that other issues -- Trump's backing for Britain's decision to leave the EU, his perceived closeness to Russia as well as his inaugural promise to put 'America first' -- also have raised 'an unbelievable number of question marks.'
Ischinger said expectations that Pence would speak at the conference on February 18 were extremely high.
Others expected to attend include Russian Foreign Minister Sergei Lavrov, Chinese Foreign Minister Wang Yi, Iranian Foreign Minister Mohammad Javad Zarif, Iraqi Prime Minister Haidar al-Abadi, and Afghan President Ashraf Ghani.
U.S. Senator John McCain, an outspoken critic of Trump's Russia policies, is among more than a dozen lawmakers expected to attend as part of a U.S. congressional delegation.
With reporting by AP, Reuters, AFP, and CNN