A man claiming to be the leader of Al Qaeda in Iraq vowed in an audiotape released Saturday to launch a monthlong offensive against U.S. troops.

There was no independent confirmation that the voice belonged to Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, but it sounded exactly like the one heard on previous audiotapes.

Al-Muhajir has been the leader of Al Qaeda in Iraq since his predecessor Abu Musab al-Zarqawi was killed in a U.S. airstrike northeast of Baghdad in 2006.

"We call on our beloved ones ... that each unit should present the head of an American as a gift to the charlatan Bush ... in addition to one of the apostate servants and slaves of the awakening (councils) during a one-month period," he said in the tape, posted on an Internet site known for its militant contents.

He made clear that the 30-day period begins from the day of the audiotape's release.

The release of the tape follows a series of deadly attacks that have raised fears of a possible Al Qaeda in Iraq resurgence. Militants have targeted members of the awakening councils, Sunni Arab tribesmen and former insurgents who changed sides and are now fighting Al Qaeda alongside U.S. forces.

On Thursday, a suicide bomber struck the funeral of two anti-Al Qaeda Sunnis north of Baghdad, killing 50 mourners. Two days earlier, suicide bombings in four major cities in northern and central Iraq killed nearly 60 people and shattered weeks of calm in Sunni-dominated areas.

The bloodshed occurred despite U.S. insistence that the Sunni insurgency is waning and that Al Qaeda, a Sunni organization, had been driven deep underground by enhanced security measures.

Saturday's tape quoted heavily from the Quran, Islam's holy book, and the sayings of the Prophet Muhammad. It contained no announcements on strategy or tactics, offering instead general advice on combat to Al Qaeda in Iraq fighters and urging them to diligently perform their religious duties.

He called on his followers to united behind his leadership and heed his counsel.

"As long as our hearts are together, obeying a leader that we trust ... then, I swear to God, if America brought all its armies and its men and women to fight us, we will win," he said.