ISTANBUL — The Syrian branch of al-Qaida has acknowledged that it captured 45 U.N. peacekeepers in southern Syria, saying it was retaliation for what the group called the United Nations’ failure to help Syria’s people during the country’s civil war.

The group, the Nusra Front, also accused the peacekeeping force, which has monitored the demarcation line between Syria and the Israeli-occupied Golan Heights since 1974, of protecting Israeli-controlled territory while doing nothing to stop the killing on the Syrian side.

The Nusra Front said it was holding 45 peacekeepers, although the United Nations had said that 44 were being held, a discrepancy that could not immediately be explained.

On Sunday, in a statement to the press, the United Nations said the 44 soldiers from Fiji remained “detained by armed elements.”

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The statement followed attacks by rebels believed to be the Nusra Front on two other bases used by 72 peacekeepers from the Philippines on Saturday. One group of 32 Philippine soldiers managed to flee after receiving backup from the mission’s “reaction force,” the U.N. said.

On Sunday, the U.N. said in the statement that the other group of 40 Philippine soldiers had left their post at night during a cease-fire between them and “the armed elements” and had reached a safe location an hour later.