The talks followed a video conference on Wednesday night in which President Obama issued instructions to Secretary of State John Kerry and Energy Secretary Ernest J. Moniz about how to complete an agreement “that meets our requirements,” the White House said in a statement.

“We’re going to resolve the last issues, if we can,” Mr. Moniz said at the start of a meeting Thursday morning with his Iranian counterpart, Ali Akbar Salehi.

“Hopefully, today is the last day,” Mr. Salehi added.