(Adds EU statement, expert level talks, Ukraine issue)
VIENNA, March 5 (Reuters) - Western powers pressed Iran on Wednesday to fully address suspicions that it may have worked on designing an atomic bomb and the United States said the issue was central to resolving the wider dispute over Tehran's nuclear programme.
The U.S. ambassador to the U.N. nuclear watchdog, Joseph Macmanus, said it remained critical for Iran to address substantively all international concerns about the so-called possible military dimensions (PMD) of the country's atomic activities.
Speaking to the 35-nation Board of Governors of the International Atomic Energy Agency (IAEA), Macmanus said a "satisfactory resolution of PMD issues will be critical to any long-term comprehensive solution to the Iranian nuclear issue".
The 28-nation European Union voiced a similar line in its statement to the board: "We urge Iran to cooperate fully with the agency regarding PMD issues, and to provide the agency with access to all people, documents and sites requested."
Iran denies Western allegations that it is seeking to develop the capability to make nuclear weapons.
The IAEA's investigation into suspected atomic bomb research by Iran is separate from, but still closely linked to, higher-level talks between Iran and six world powers aimed at reaching a final settlement of the decade-old nuclear dispute.
In Vienna later on Wednesday, experts from Iran and the six powers - the United States, Russia, France, Britain, Germany and Britain - were to meet to prepare for the next round of political-level talks on March 17, also in the Austrian capital. Diplomats said Russia would take part in the meeting, suggesting no apparent immediate fallout in the Iran negotiations because of the crisis over Ukraine.
"The overriding commitment is one of working together to resolve the Iran nuclear programme and there are many other issues in the world that will continue to cause us to have disagreements and debates and sometimes to find ourselves in opposition to one another," Macmanus told reporters when asked whether tensions over Ukraine could disrupt the Iran talks. (Reporting by Fredrik Dahl; Editing by Mark Heinrich)