New Delhi, Jan. 31 -- 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 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.

Those coverings block satellites from seeing what's happening on the ground - right now the only way for inspectors from the International Atomic Energy Agency to monitor the sites as...