The leader of the Islamic State, Abu Bakr al-Baghdadi, resurfaced on Wednesday in the first audio recording of him to be released in nearly a year, one in which he called on followers to attack Westerners with knives, guns, cars and bombs.

Based on events cited in the recording, it appears to have been made within the past few weeks, according to the SITE Intelligence Group, which tracks the group’s propaganda online and provided a translation.

If deemed authentic, the speech should serve to quell rumors of Mr. Baghdadi’s death. Counterterrorism officials in the United States and Europe have long said that they believed Mr. Baghdadi was still alive, though repeated online rumors suggested he had died, including in a Russian airstrike.

In the nearly one-hour speech, Mr. Baghdadi sought to shift attention away from the group’s battlefield losses and his shrinking caliphate. In Iraq and Syria, the Islamic State has lost all but 2 percent of the territory once held, an area the size of Britain.