WASHINGTON — The New York Times is reporting that the Obama administration learned in November about the photographs said to document widespread torture and executions in Syrian prisons when a State Department official viewed some of the images on a laptop belonging to an anti-Syrian-government activist, a senior official said Wednesday.

The United States did not act on the photos, officials told the Times, because it did not have possession of the digital files and could not establish their authenticity. Nevertheless, they said, the administration believes the photos are genuine, basing that assessment in part on the meticulous way in which the bodies in the photos were numbered.

The photographs, some of which were released this week on the eve of an international peace conference on Syria, have helped prompt the administration to heighten its demand that President Bashar al-Assad release political prisoners and allow Red Cross inspectors access to the prisons, the Times reported.

At the White House, press secretary Jay Carney said: “These photos cannot be ignored or dismissed. They suggest widespread and apparently systematic violations of international human law, and demonstrate just how far the regime is willing to go in harming its own people.’’

Administration officials told the Times that the State Department official, whom they did not name, viewed the photos in Turkey during a meeting with the representative of an antigovernment group.

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