The Italian government on Thursday deplored the death of an Italian aid worker in a U.S. airstrike, calling it a "fatal error" by the Americans.

Italian Premier Matteo Renzi expressed his "profound pain" over Giovanni Lo Porto's death and offered Italy's condolences to Lo Porto's family and that of American Warren Weinstein, who was killed in the same airstrike on the border between Pakistan and Afghanistan. Both were held hostage by al-Qaida.

President Barack Obama said Thursday they were killed in a January strike on what the U.S. believed was an al-Qaida compound with no civilians present.

In a statement, Renzi said Obama had informed him of the death in a phone call Wednesday and that Lo Porto's family was subsequently informed.

Italy's Foreign Ministry called Lo Porto a "generous and expert volunteer" who was working in Pakistan for Welthungerhilfe, a German aid group, when he was taken hostage in 2012.

The Foreign Ministry said it had worked for three years to track him down and return him to his family.

"The conclusion unfortunately was different because of the tragic and fatal error of our American allies recognized by President Obama," the ministry said in a statement.

"We're shattered by today's news," Simone Pott, a spokeswoman for Welthungerhilfe, told The Associated Press. "So much was done to try and get him released," she said, without elaborating.

Lo Porto had joined the aid group in October 2011 and was working as a project manager in Pakistan's Multan region when he was kidnapped in January 2012, together with German Bernd Muehlenbeck.

Muehlenbeck was freed last year in circumstances that Pott declined to comment on.

Asked whether the group blamed the U.S. for Lo Porto's death, Pott said: "At this stage we're just trying to get more information."

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Associated Press writer Frank Jordans in Berlin contributed to this report.report.