The U.N. organization last week said a group had posted online e-mail addresses of specialists connected to the agency. The breached computer server has been taken offline and the situation is still being probed, Amano said during an event in Washington. The group did not access data related to agency monitoring of nuclear work by member nations.
"If you ask if this is the only case? I would say there have been some other tries but we are doing our best to protect our system," Amano said.
The group uses a name that appears to be Iranian and called for an agency examination of Israel's atomic operations.
"The group ... they have what looks like an Iranian name. But that does not mean that the origin is Iran," according to Amano.
Amano's agency continues to probe Iran's atomic operations, which are suspected in Washington and elsewhere of being aimed at producing a nuclear-weapon capacity. Iran has rejected those claims, and has highlighted the widely accepted assumption that Israel holds the Middle East's sole nuclear arsenal.