Secretary of State Antony J. Blinken is set to depart on Tuesday for Brussels, where he will attend meetings with NATO and European officials to discuss Ukraine’s war against Russia, the State Department announced.

Mr. Blinken’s trip, a late addition to his schedule before a trip to Latin America, comes amid grave concern among Ukraine’s supporters that the new Trump administration will slash U.S. support for Kyiv.

The Biden administration and NATO officials also fear that President-elect Donald J. Trump may try to undermine the military alliance and even seek to withdraw the United States from it.

The State Department said Mr. Blinken would meet NATO and E.U. counterparts “to discuss support for Ukraine in its defense against Russia’s aggression.”

Mr. Blinken plans to travel on to Peru and Brazil, where he will join President Biden for the annual Asia-Pacific Economic Cooperation summit and the Group of 20 Leaders’ Summit.