VIENNA — As a high-level team of Iranian officials flew here on Tuesday for what appears to be an intensive final week of negotiations for a comprehensive nuclear accord, President Obama issued a warning that he was prepared to walk away from any agreement with a verification regime that consisted of “a few inspectors wandering around every once in a while.”

The return here of Iran’s foreign minister, Mohammad Javad Zarif, was notable because it followed high-level consultations in Tehran. He was accompanied by Ali Akbar Salehi, the head of Iran’s Atomic Energy Organization, who has been ill but played a pivotal role in previous rounds of talks.

Hossein Fereydoun, a younger brother of President Hassan Rouhani, who has appeared here at other turning points, was also on Mr. Zarif’s plane.