U.S. President Barack Obama is expected to reinforce U.S.-EU opposition to Russia's annexation of Crimea and push for speeding up trade talks with the European Union.
Obama is due to attend a summit on March 26 between the United States and the European Union in Brussels, where he will give a keynote speech on trans-Atlantic relations.
On March 25, Obama said Russia's actions in Ukraine were a sign of weakness. He was speaking at a news conference in The Hague after a nuclear security summit.
"Russia is a regional power that is threatening some of its immediate neighbors not out of strength but out of weakness," said Obama.
"Ukraine is a country in which Russia has had enormous influence for decades, since the breakup of the Soviet Union. And we have considerable influence on our neighbors. We generally don't need to invade them in order to have strong cooperative relationships with them. The fact that Russia felt compelled to go in militarily and laid bare these violations of international law indicates less influence not more," Obama concluded.
In a joint statement issued at the nuclear summit, the United States and Ukraine said Russia's actions in Crimea "undermine the foundation of the global security architecture and endanger European peace and security."
Obama warned that the United States and its allies will not back down from imposing further sanctions on Moscow.
Obama also voiced concern about the massing of numerous Russian troops on the border with Ukraine, but admitted that Russia had the right to deploy troops on its own territory.
In Brussels, NATO Secretary-General Anders Fogh Rasmussen echoed Obama's preoccupation with the Russian buildup near Ukraine.
"I can assure you that we are very much concerned about the Russian military buildup along the borders of Ukraine," said Rasmussen. "We are, as an alliance, focused on providing effective deterrence and defense. And all NATO allies can be assured of our determination to provide effective defense."
Obama and Rasmussen are due to hold talks in Brussels on the sidelines of the U.S.-EU summit.
During the summit, EU leaders are also expected to press Obama to help reduce Europe's dependence on Russian energy through exports of U.S. natural gas. Russia provides around one-third of the EU's oil and gas and some 40 percent of the gas is exported through Ukraine.
The summit comes amid stalled negotiations for a proposed free-trade U.S.-EU agreement, dubbed the trans-Atlantic Trade and Investment Partnership (TTIP), which would be the world's biggest accord of its kind. However, eight months into talks, negotiators remain far apart on many issues.
Obama is expected to underline the need to strengthen trans-Atlantic ties in a key speech before 2,000 guests in one of the city's museums.
Earlier on March 26, the U.S. president toured and spoke briefly at a World War I battlefield in Flanders where U.S. soldiers fought almost a century ago.
Obama laid a wreath at a memorial there and said Belgium and the United States stand together forever for freedom, dignity, and the triumph of the human spirit.
He said the lessons of World War I are still relevant, pointing to ongoing efforts to rid Syria of chemical weapons, which were also used in Flanders.
Based on reporting by AFP and Reuters