BRUSSELS (Reuters) - U.S. ambassadors to the European Union and NATO sought to reassure Washington's allies in Europe on Wednesday that close cooperation would continue following the election of Donald Trump as president.

"There's a lot of continuity here," NATO ambassador Douglas Lute told a gathering of European diplomats at the U.S. embassy in Brussels. "NATO has always been a bipartisan venture for the United States."

During his campaign, the Republican Trump questioned U.S. spending on European defense through NATO and European leaders, especially those closest to Russia in the east, are concerned.

EU ambassador Anthony Gardner, appointed by outgoing Democrat President Barack Obama, urged Europeans not to make assumptions about the nature of a Trump administration: "It's too early to reach conclusions," he told reporters.

"Any U.S. administration is going to realize the importance of ... U.S.-EU relations. Give it time," he said.

(Reporting by Alastair Macdonald)