WASHINGTON / PARIS (Reuters) — The United States on Thursday imposed sanctions on Iran’s nuclear entity and its top official, the Treasury Department said, but sources said it will allow Russian, Chinese and European firms to continue work at Iranian nuclear sites to make it harder for that country to develop a nuclear weapon.

The Trump administration will let the work go forward by issuing waivers to sanctions that bar non-U.S. firms from dealing with the Atomic Energy Organization of Iran, the sources said on condition of anonymity. The waivers’ renewal for 60 days will allow non-proliferation work to continue at the Arak heavy-water research reactor, the Bushehr nuclear power plant, the Tehran Research Reactor and other nuclear cooperation initiatives.

“There was a difference of opinion between the U.S. Treasury and State Department. The Treasury won”, said a Western diplomat familiar with the issue. “There is an appetite for more sanctions, so this was a surprise; but others argue that these waivers are vital to ensure non-proliferation.” The diplomat said the U.S. had likely opted to extend the Bushehr waiver because the Russian company targeted also provides nuclear fuel to U.S. facilities, causing a potential sanctions headache for the administration.

A U.S. official confirmed the waivers.

Ali Akbar Salehi, head of the Atomic Energy Organization of Iran, and the organization itself have been placed under U.S. sanctions, according to the Treasury’s website.