Iranian President Hassan Rouhani threatened reduce cooperation with the International Atomic Energy Agency, the U.N.’s nuclear watchdog, amid escalating tensions with the United States.

“Iran’s nuclear activities have always been for peaceful purposes, but it is Iran that would decide on its level of cooperation with the IAEA,” Iranian state news agency IRNA quoted Rouhani as saying after meeting IAEA head Yukiya Amano in Vienna, Reuters reported.

“The responsibility for the change of Iran’s cooperation level with the IAEA falls on those who have created this new situation,” he added.

Rouhani is in Europe to meet with the remaining signatories of the Iranian nuclear deal: the United Kingdom, France, Germany, Russia and China.

While in Switzerland, Rouhani told Swiss President Alain Berset that he considers Israel “illegitimate” after the Swiss leader press Rouhani on the necessity of officially recognizing Israel.

“Yesterday I told him frankly that Iran considers the Zionist regime illegitimate, and its actions in the region aggressive and condemnatory,” said Rouhani, the semi-official Iranian Students’ News Agency reported.

The statements by Rouhani come amid escalating tensions with the United States since it pulled out of the Iranian nuclear agreement in early May and re-imposed harsh sanctions on Tehran. The Trump administration has told countries that it must stop buying oil from Iran by Nov. 4 or face getting caught up in U.S. sanctions.

An Iranian Revolutionary Guards commander said on Wednesday that Iran would block all oil shipments in the Persian Gulf through the Strait of Hormuz in retaliation for any U.S. actions to end Iranian oil sales.

“If they want to stop Iranian oil exports, we will not allow any oil shipment to pass through the Strait of Hormuz,” said Ismail Kowsari.