Nato chief Anders Fogh Rasmussen has said Americans should set aside any doubts about the commitment of other Nato members to the war in Afghanistan.
In his first speech in the US as secretary-general, Mr Rasmussen said the campaign in Afghanistan was one of necessity, not choice.
The speech comes after the top US and Nato commander in Afghanistan warned of likely failure without more troops.
But rising casualty figures have hit public support for the operation.
Mr Rasmussen pointed out 40% of the Nato troops involved in the operation were from non-US countries and that soldiers from more than 20 countries had been killed.
Shoring up the coalition is what this visit is all about, says the BBC's Paul Adams in Washington, and with that end in mind, Mr Rasmussen carefully avoided taking sides in the American troop debate.
He didn't say, and it is not clear, whether he thinks additional troops are the answer, our correspondent notes.
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