The Trump administration on Friday renewed five of seven sanctions waivers that allow Russia and European nations to conduct civilian nuclear cooperation with Iran, even as the U.S. steps up the pressure on Tehran, a senior U.S. official said.

The waivers, which were due to expire Saturday, are being extended for between 45 days and 90 days, shorter periods than had been granted in the past. But they will permit work at several Iranian nuclear sites to continue without U.S. penalties. Under the terms of the 2015 Iran nuclear deal, Russia and several European nations help to maintain the facilities and are engaged in converting equipment there for exclusively civilian use.

Facilities included in the waiver extensions include the Bushehr nuclear power plant, the Fordow enrichment facility, the Arak nuclear complex and the Tehran Research Reactor, the official said.

The official, who was not authorized to discuss the matter publicly and spoke on condition of anonymity, said the other two waivers — one that allowed Iran to store heavy water in Oman and the other that allowed Russia to process Iranian uranium — are not being renewed.

President Donald Trump withdrew the U.S. from the Iran nuclear deal last year, reimposed sanctions that had been eased in November and has steadily ramped up pressure on Iran in the months since.

Last month, his administration announced it would no longer renew sanctions exemptions that allowed China, India, Japan, Turkey and South Korea to continue importing Iranian oil. Those waivers expired Friday, although it was not immediately clear whether the administration would impose sanctions on some or all of those countries if they take delivery of previously purchased oil.

Some hard-liners on Iran in Congress and outside the administration have called for the elimination of all sanctions waivers, including for civilian nuclear cooperation, in order for the administration to make good on its "maximum pressure" campaign.

Supporters of the Iran deal say the cooperation waivers are important to maintain because they give the outside world additional eyes on what Iran is doing in its nuclear facilities.