KABUL (Reuters) - A U.S. investigation into reports of civilian casualties caused by an air strike near the northern city of Kunduz last month concluded that there was no substance to the allegations, the U.S. military said on Friday.

The investigation was launched last month following reports that as many as 14 civilians had been killed in an air strike supporting an operation by Afghan security forces in Chardara district, outside Kunduz city on July 19.

“After carefully considering all relevant and reasonably available information, which included a review of the Afghan government’s report of findings, our investigation found no credible information to corroborate the allegations,” U.S. Army Lt. Col. Martin O’Donnell, U.S. Forces-Afghanistan spokesman, said in a statement.

“U.S. Forces-Afghanistan takes all allegations of civilian casualties seriously. Should any further credible information become available, an investigative body will reconvene to re-review this allegation,” the statement said.

Afghan government officials said last month that as many as 14 civilians had been killed but said that the causes of their deaths was unclear.

A statement from the U.S. military last month confirmed that U.S. forces had conducted strikes in support of Afghan-led ground operations but said that its on-the-ground assessment gave no indications that they had caused civilian casualties.

According to U.N. figures, civilian casualties from air strikes rose by 52 percent in the first half of the year following a sharp jump in the number of aerial operations launched under a U.S. strategy aimed at forcing the Taliban to accept peace negotiations.