ABU DHABI, United Arab Emirates — Secretary of State John Kerry came up a few disputed words short of closing a landmark nuclear deal with Iran on Sunday in Geneva. Now he is defending the diplomacy that led to that near miss against a rising chorus of critics at home and abroad.

On Monday, in this Persian Gulf emirate deeply suspicious of a nuclear Iran, Mr. Kerry laid out his fullest argument yet.

“Having the negotiation does not mean giving up anything,” he declared at a news conference after meeting top officials of the United Arab Emirates. “It means you will put to the test what is possible and what is needed, and whether or not Iran is prepared to do what is necessary to prove that its program can only be a peaceful program.”

Mr. Kerry promised America’s allies in the Middle East that a nuclear accord would not put their security at risk, and he pleaded with critics of a deal, most notably Prime Minister Benjamin Netanyahu of Israel, not to try to scuttle it before the details are even hammered out.