U.S. President Barack Obama says the United States and Europe are united in imposing a cost on Russia for its actions in Ukraine.

Mr. Obama made the comments to reporters in the Netherlands ahead of an emergency meeting of the Group of Seven, or G-7 focused on Russia's annexation of Crimea. Analysts say the session appears aimed at coordinating Western sanctions imposed on Moscow since Russian troops crossed into Crimea earlier this month. The group is also expected to further evaluate the cost of possible retaliatory measures by Moscow.

President Obama said Monday that Europe and the United States were united in support of the Ukrainian government and the Ukrainian people. The comments came after he met with Dutch Prime Minister Mark Rutte in Amsterdam.

A two-day nuclear security summit in the Hague which started Monday was set to be the highlight of the American president's weeklong trip to Europe and Saudi Arabia, before being overshadowed by developments in Ukraine.

Japan and the U.S. pledged Monday to remove and dispose all highly-enriched uranium and separated plutonium from the Fast Critical Assembly at the Japan Atomic Energy Agency.

Mr. Obama will meet with Chinese President Xi Jinping on the sidelines of the nuclear summit Monday.

On Tuesday, he will take part in a three-way summit with Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-Hye.

Meanwhile, U.S. Secretary of State John Kerry is set to meet Monday with Russian Foreign Minister Sergei Lavrov.