Bloomberg reports: Iran’s “workshops” for making nuclear centrifuges and components for the devices are widely dispersed and hidden, adding to the difficulties of a potential military strike by Israel, according to a new report by U.S. congressional researchers.

Neither Israel nor the U.S. is certain of the locations of all such facilities, analysts at the Congressional Research Service wrote in the report obtained today. The analysts cited interviews with current and former U.S. government officials familiar with the issue who weren’t identified.

Israel’s capability to halt or set back Iran’s nuclear program through a military strike has been central to the debate over whether Israel should undertake such a mission alone. While President Barack Obama has urged more time for economic sanctions to work, Israeli officials led by Prime Minister Benjamin Netanyahu and Defense Minister Ehud Barak say it may soon be too late to prevent Iran from developing the capability to produce a nuclear weapon.

The possibility of dispersed facilities complicates any assessment of a potential raid’s success, making it “unclear what the ultimate effect of a strike would be on the likelihood of Iran acquiring nuclear weapons,” the report found.

A U.S. official said in April 2011 that there “could be lots of workshops’ in Iran,” the authors said. Last month, a former U.S. government official with “direct experience” in the issue told the researchers that “Iran’s centrifuge production is widely distributed and that the number of workshops has probably multiplied ‘many times’ since 2005 because of an increase in Iranian contractors and subcontractors working on the program.”

“An attack that left Iran’s conversion and centrifuge production facilities intact would considerably reduce” the time Iran would need to resume its nuclear work, said the congressional researchers led by Jim Zanotti, a Middle Eastern affairs specialist. He wrote the report with analysts Kenneth Katzman, Jeremiah Gertler and Steven Hildreth.

Israel, the U.S. and European allies say they are concerned that Iran may begin trying to produce the highly enriched uranium needed for a nuclear weapon. Iran says its nuclear program is intended solely to generate power and for medical research. Centrifuges spin at high speeds to separate uranium isotopes.

Michael Hayden, a former director of the Central Intelligence Agency, said in January “that neither the U.S. nor Israel knows the location of all key Iranian nuclear-related facilities,” according to the congressional researchers.

Assessments vary on how much impact a military attack would have on Iran’s centrifuge facilities. An executive branch official who wasn’t named told the research service last month that Iran doesn’t have enough spare centrifuges or components to install new devices immediately, the authors wrote. A former official said the same day that Iran probably could rebuild or replicate most centrifuge workshops within six months, the researchers said.