(CNN) -- New imagery posted on Google Earth shows evidence Iran continues to build out its nuclear sites, according to a group focused on stopping the spread of nuclear weapons and related technology.
The Institute for Science and International Security said Tuesday it had examined updated commercial satellite imagery of Iran and found evidence of slow, but continuing, build-out of nuclear facilities.
Iran has a controversial nuclear program. Many world powers say it aspires to building nuclear weapons but the country says it is developing nuclear power for peaceful purposes. The U.N. Security Council has imposed sanctions on Iran in an effort to curb its nuclear program.
ISIS says images of the Arak heavy water reactor and heavy water production facility from June 2010 appeared on Google Earth.
"Compared with earlier imagery from November 2009, also available on Google Earth, there do not appear to be major external changes at either reactor site or the heavy water production facility," ISIS said.
However, it said, "construction continues inside the buildings" and "assorted activity at heavily guarded sites along the mountainside to the Arak site" continues.
Google Earth in July posted images of the Gchine mine and mill from November 2010.
"There do not appear to be any new ponds under construction," ISIS said. But it says the "waste tailings level can be seen changing."
In August, Google Earth added images of the Ardakan yellowcake production plant from March.
"The facility is being constructed very slowly, with few buildings added each year. Comparing the imagery to a picture from October 2009, a few more buildings have been constructed," ISIS said.
The institute said "two large square excavations can be seen," and "one or both of them could be for a tailing pond." Tailings are materials left over after ore is processed.
Last month, ISIS and other groups leaked an International Atomic Energy Agency report saying Iran continues to defy U.N. resolutions aimed at curbing its nuclear program and cited "increasing" concerns it may be developing nuclear weapons.
It follows a visit last month by an IAEA official to Iran, at the Middle Eastern nation's invitation. The report's author notes some instances in which Iran appears to be working with the international agency, as well as conducting parts of its program as it had said it would.
But the report, intended for the IAEA's director general as well as the U.N. Security Council, also suggests Iran continues to flout U.N. and other resolutions regarding its nuclear program.