Abu Abdullah Rashid al-Baghdadi, the head of the Mujahidin Shura Council - which consists of five anti-US and anti-government groups including al-Qaeda in Iraq - described al-Zarqawi's death as a "great loss".
The tape aired on Friday appears to be an attempt to rally support for the Sunni fighters. "This is a message to the enemies of God, the Crusaders, the rejectionists and the renegades," the voice says, referring to the US-led forces, the Shias, and the Sunnis in the Iraqi government.
"The martyrdom of the leader [al-Zarqawi] will not change the arena of confrontation. Rather, it will become fiercer and stronger," al-Baghdadi says. Al-Zarqawi was killed when by a US air strike on the house in Baquba where he was meeting his advisers on June 7.
"This leader [al-Zarqawi] has laid the foundations and his great loss will not lead to weakness. He will remain a symbol for all the mujahideen, who will take strength from his steadfastness," he says.
Al-Baghdadi is believed to be a former officer in Saddam's army, or its elite Republican Guard, who worked with al-Zarqawi after the overthrow of the Iraqi president in April 2003.
US calls this man al-Masri, but an
expert says he is Yusif al-Dardiri
Some terror experts mentioned al-Baghdadi as the possible successor to al-Zarqawi, but the US military believe al-Qaeda in Iraq is now led by Abu Ayyub al-Masri, an Egyptian-born fighter who trained with al-Zarqawi in Afghanistan.
Al-Qaeda in Iraq has identified its new leader as Abu Hamza al-Muhajer.
Multinational and Iraqi forces have carried out a number of raids targeting anti-government Sunni fighters since al-Zarqawi's death. The US military says 104 fighters have been killed and 28 significant arms caches discovered.
On Friday, Muntasir al-Zayyat, an expert on Islamist groups, told Aljazeera that the purported new leader of al-Qaeda in Iraq whose picture was published by the US forces in Iraq, is actually Yusif al-Dardiri, an Egyptian in his mid-30s from the southern Egyptian city of Sohaj.
Al-Dardiri's family moved to Cairo while he left Egypt in the late 1980s for another Arab country, al-Zayyat said.