KABUL, Afghanistan — The leader of Al Qaeda, Ayman al-Zawahri, broke nearly a year of radio silence on Thursday to pledge allegiance to the new leader of the Taliban, but his audio message made no mention of the Taliban’s two-year delay in acknowledging that their former leader was dead.

Mr. Zawahri’s message came in an audio recording attached to a Twitter message, according to the SITE Intelligence Group, a terrorist monitoring organization, which said it was an unusual way for him to distribute messages. Mr. Zawahri, a 64-year-old Egyptian, took over Al Qaeda after American commandos killed Osama bin Laden in 2011, but he has not had any confirmed audio or video communications since September.

SITE said the voice on the new audio message, which acknowledged that the Taliban had chosen Mullah Akhtar Muhammad Mansour as their new leader to replace the deceased Mullah Muhammad Omar, sounded like that of Mr. Zawahri. But it did little to dispel speculation, even among some fellow jihadists, that the Qaeda leader was himself dead.

Leaders of extremist groups involved in the Afghan war have undermined their credibility among many followers after news emerged that senior figures have been dead for months or even years. In addition to Mullah Omar, who died in April 2013, an ally, Jalaluddin Haqqani, head of the extremist Haqqani network, reportedly died in December, but the group continues to deny that.