The reporter behind the report of a Russian missile in Poland is no longer at The A.P.

When The Associated Press wrote last week that Russia had struck a village in Poland with a missile, fears quickly rose the event would escalate the Ukraine-Russia war into an even bigger conflict.

But it soon appeared that Russia did not fire the missile. And one of the journalists behind the article is now no longer at the news organization.

The reporter, James LaPorta, who had worked at The A.P. since April 2020, had provided information that Russia was to blame from a single U.S. intelligence source. The A.P. used that information in a news alert: “A senior U.S. intelligence official says Russian missiles crossed into NATO member Poland, killing two people.”

The significance of the alleged event was immediately apparent: It could escalate the war.

The information was soon proven wrong. The NATO secretary general and Polish officials said the explosion was most likely caused by a Ukrainian air-defense missile that was fending off a Russian attack and went off course.

The A.P. corrected the article the next day, stating that the erroneous report was “based on information from a senior American intelligence official who spoke on condition of anonymity.”

The correction said: “Subsequent reporting showed that the missiles were Russian-made and most likely fired by Ukraine in defense against a Russian attack.”

In a response to questions about Mr. LaPorta, Lauren Easton, a spokeswoman for The A.P., said in a statement, “When our standards are violated, we must take the steps necessary to protect the integrity of the news report. We do not make these decisions lightly, nor are they based on isolated incidents.”

Mr. LaPorta declined to comment for this article.

In a tweet on Tuesday, Mr. LaPorta thanked “the multitude of journalists, editors and long-time readers that have reached out to me with words of encouragement and kindness. It sincerely means the world.”

Mr. LaPorta covered national security and the U.S. military for The A.P. He previously worked as a reporter for Newsweek, Frontline PBS, United Press International and the Daily Beast. He is a Marine Corps veteran and served in the Afghanistan war. According to his LinkedIn profile, he was a military adviser for the NBC show “This Is Us.”

The news of Mr. LaPorta’s departure from The A.P. was reported earlier by The Daily Beast.