Satellite photos show activity at Iran nuclear sites as tensions rise over protest crackdown

As tensions soar over Iran's bloody crackdown on nationwide protests, satellite images show activity at two Iranian nuclear sites bombed last year by Israel and the United States that may be a sign of Tehran trying to obscure efforts to salvage any materials remaining there.

The images from Planet Labs PBC show that roofs have been built over two damaged buildings at the Isfahan and Natanz facilities, the first major activity noticeable by satellite at any of the country's stricken nuclear sites since Israel's 12-day war with Iran in June.

Roofs seen in Isfahan and Natanz

Those coverings block satellites from seeing what's happening on the ground — right now, it's the only way for inspectors from the International Atomic Energy Agency to monitor the sites, as Iran has prevented access.

The new roofs do not appear to be a sign of reconstruction starting at the heavily damaged facilities, experts who examined the sites said. Instead, they are likely part of Iran's efforts "to assess whether key assets — such as limited stocks of highly enriched uranium — survived the strikes," said Andrea Stricker, who studies Iran for the Washington-based Foundation for Defense of Democracies, which has been sanctioned by Tehran.

"They want to be able to get at any recovered assets they can get to without Israel or the United States seeing what survived," she said.

The main above-ground enrichment building at Natanz was known as the Pilot Fuel Enrichment Plant. Israel hit the building on June 13, leaving it "functionally destroyed," and "seriously damaging" underground halls holding cascades of centrifuges, the IAEA's director-general, Rafael Mariano Grossi, said at the time. 

A U.S. follow-up attack on June 22 hit Natanz's underground facilities with bunker-busting bombs. Grossi told "Face the Nation with Margaret Brennan" that intelligence out of Iran shows that the follow-up U.S. strikes caused "severe damage," but not "total damage." 

"Iran has the capacities there; industrial and technological capacities. So if they so wish, they will be able to start doing this again," Grossi said.

Planet Labs PBC images show Iran began in December to build a roof over the damaged plant. It completed work on the roof by the end of the month. Iran has not provided any public acknowledgment of that work. Natanz's electrical system appears to still be destroyed.

At Isfahan, Iran began building a similar roof over a structure near the facility's northeast corner, finishing the work in early January. The exact function of that building isn't publicly known, although the Israeli military at the time said its strikes at Isfahan targeted sites there associated with centrifuge manufacturing. The Israeli military did not respond to requests for comment over the construction.

Meanwhile, imagery shows that two tunnels into a mountain near the Isfahan facility have been packed with dirt, a measure against missile strikes that Iran also did just before the June war. A third tunnel appears to have been cleared of dirt, with a new set of walls built near the entrance as an apparent security measure.

Sarah Burkhard, a senior research associate for the Washington-based Institute for Science and International Security, which long has watched Iran's nuclear sites, said the roofs appear to be part of an operation to "recover any sort of remaining assets or rubble without letting us know what they are getting out of there."

Sean O'Connor, an expert at the open-source intelligence firm Janes, concurred that the aim was likely "to obscure activity rather than to, say, repair or rebuild a structure for use."

Iran has not publicly discussed the activity at the two sites. The IAEA, a watchdog agency of the United Nations, did not respond to requests for comment.

U.S. President Trump repeatedly has demanded that Iran negotiate a deal over its nuclear program to avert threatened American military strikes over the country's crackdown on protesters. The U.S. has moved the USS Abraham Lincoln and several guided-missile destroyers into the Middle East, but it remains unclear whether Mr. Trump will decide to use force.

Mr. Trump said earlier this month that the "armada" of warships was headed toward Iran "just in case."

The Lincoln was in the Pacific when the president first issued a warning on social media that the U.S. was "locked and loaded" to hit Iran if the regime killed anti-government protesters.

Since the demonstrations began, the Human Rights Activists in Iran, a U.S.-based non-governmental organization, estimates that more than 4,000 protesters have been killed so far and says that number is likely to rise. Two sources, including one inside Iran, told CBS News earlier this month that at least 12,000, and possibly as many as 20,000 people have been killed.