A chorus of senior Iranian officials — from the director of civil aviation to the chief government spokesman — issued statement after statement rejecting the allegations, their claims amplified on state media.

The suggestion that Iran would shoot down a passenger plane was a “Western plot,” they said, “psychological warfare” aimed at weakening Iran just as it had exercised its military muscle against the United States.

But in private, government officials were alarmed and questioning whether there was any truth to the Western claims. Mr. Rouhani, a seasoned military strategist himself, and his foreign minister, Javad Zarif, deflected phone calls from world leaders and foreign ministers seeking answers. Ignorant of what their own military had done, they had none to give.

Domestically, public pressure was building for the government to address the allegations.

Among the plane’s passengers were some of Iran’s best and brightest. They included prominent scientists and physicians, dozens of Iran’s top young scholars and graduates of elite universities, and six gold and silver medal winners of international physics and math Olympiads.

There were two newlywed couples who had traveled from Canada to Tehran for their weddings just days earlier. There were families and young children.

Their relatives demanded answers. Iranian social media began to explode with emotional commentary, some accusing Iran of murdering its own citizens and others calling such allegations treason.

Persian-language satellite channels operating from abroad, the main source of news for most Iranians, broadcast blanket coverage of the crash, including reports from Western governments that Iran had shot down the plane.