On the eve of the release of a report by the International Atomic Energy Agency on Iran, Chancellor Angela Merkel of Germany and President Nicolas Sarkozy of France have threatened tough new sanctions if Iran does not demonstrate a willingness to negotiate on its nuclear program.

Speaking on Thursday at a news conference in Berlin with Prime Minister Benjamin Netanyahu of Israel, Mrs. Merkel raised the possibility of new penalties against Iran in the energy and financial sectors.

“If there is no positive answer by September, we will have to consider further measures,” she said, according to Reuters.

The United States has given Iran until September to give up nuclear enrichment in return for talks on economic incentives — or face tougher sanctions.

Echoing the growing impatience with Iran’s reluctance to enter into negotiations, Mr. Sarkozy has also been talking about the possibility of what he called “severe” new sanctions against Iran and stronger inspection powers for the atomic energy agency if Iran did not cease its nuclear activities.

“There are the same leaders, in Iran, who tell us that the nuclear program is peaceful and that the elections were honest,” he said in his annual address to France’s ambassadors on Wednesday. “Frankly, who believes them?”