Holder says he condemns the disclosures as having put the nation's security at risk as well as the safety of diplomats and other U.S. government personnel.
The attorney general made the comments to reporters at a news conference on another topic.
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Hoekstra: World's Trust in U.S. Now at Risk
U.S. Encouraged Diplomats to Spy, Leaks Show
Leaked Cables Shine Light on Iran Nuclear Threat
"We have an active, ongoing criminal investigation with regard to this matter," Holder said. "We are not in a position as yet to announce the result of that investigation, but the investigation is ongoing."
"I think there's a real basis, there's a predicate for us to believe that crimes have been committed here and we are in the process of investigating those crimes," he said.
Holder seemed to praise journalists who show restraint by essentially seeking government permission before disclosing anything of importance - and to criticize the outlets that facilitated WikiLeaks' unsanctioned release.
"Members of the press, people who come into possession of this information, I think - hope -would act in a responsible manner," Holder said. "I think that has clearly not happened here. And there are consequences, real consequences."
Links to Leaked Cables:
Cables Shine Light Into Secret Diplomatic Channels (NYT)
The US Embassy Cable (Guardian)
A Superpower's View of the World (Spiegel, in English)
Los papeles del Departamento de Estado (El Pais)