A visit by international nuclear inspectors to Iran ended in failure Tuesday. Tehran not only blocked access to a site the inspectors believe could have been used for tests on how to produce a nuclear weapon, they reported, but it also refused to agree to a process for resolving questions about other “possible military dimensions” to its nuclear program.

The announcement came in a terse press release from the International Atomic Energy Agency, a United Nations agency, which said its inspection team had left the country. The agency is expected to release its latest report on the status of Iran’s program in the next week.

The inspectors’ previous visit to Iran ended several weeks ago with no agreement other than to meet this week.

Iran’s refusal to deal with the inspectors’ questions is likely to increase tension, at a moment of heightened sanctions and after the assassination of nuclear scientists in Iran and suspected retaliation against Israeli diplomats. Iran struck an increasingly bellicose tone on Tuesday, with an Iranian official warning that the country would take pre-emptive action against perceived foes if it felt its national interests were threatened. The country also laid down new conditions for oil sales.