The International Atomic Energy Agency (IAEA) said today it had confronted Iran with Western intelligence reports and Tehran had not so far explained documents pointing to undeclared efforts to "weaponize" nuclear materials by linking uranium processing with explosives and designing a missile warhead.
Mr Olmert arrived in Tokyo today on his first visit to Japan as prime minister. He will meet US Secretary of State Condoleezza Rice in the Japanese capital on Thursday.
The IAEA report showed Iran was continuing with a nuclear weapons programme and the UN Security Council should impose more sanctions, the Israeli prime minister said.
"If we had formulated the report, we would have made it sharper," Mr Olmert told reporters on the flight to Tokyo, where he will stay until Thursday.
"The basic fact doesn't change. There is a plan to create non-conventional weapons. It must be stopped."
The IAEA findings, which also said Iran had failed to clear up all outstanding questions by an agreed February deadline, may spur the Security Council to adopt a third round of sanctions against the Islamic Republic as early as this week.
The United States, which has accused Iran of having a secret programme to build nuclear weapons, said the IAEA's report had produced a good reason to impose new sanctions.