VIENNA — The head of a U.N. nuclear team traveling to Iran on Saturday urged the country to work with his mission on probing Tehran’s alleged attempts to develop an atomic arms program, adding such cooperation is long overdue.

The unusually blunt comments by International Atomic Energy Deputy Director General Herman Nackaerts reflected the importance the IAEA is attaching to the chief focus of the trip — ending more than three years of Iranian refusal to answer questions about such suspicions.

Nackaerts told reporters at Vienna airport he hopes Iran “will engage with us on all concerns.”

“So we’re looking forward to the start of a dialogue,” he said: “A dialogue that is overdue since very long.”

Diplomats said Iran had accepted the inclusion of two senior weapons experts — Jacques Baute of France and Neville Whiting of South Africa — with relatively little fuss. That suggests the Islamic Republic may be prepared to address some issues related to the allegations.