In a separate stand-off, Turkey rejected demands by militants holding three Turkish hostages.
The family of Corporal Wassef Ali Hassoun confirmed he was the kidnapped marine who appeared in a videotape shown on Sunday. The US military said Cpl Hassoun, a Muslim of Middle Eastern origin, was last seen June 19 and did not report for duty the next day.
Cpl Hassoun had gone "on an unauthorised absence", said Brigadier General Mark Kimmitt, the coalition deputy operations chief, giving few details. "Based on his personal situation, there was reason to suspect that he was heading over to Lebanon." Brig Gen Kimmitt said the military was investigating.
The hostage had a white blindfold covering his eyes and wore military fatigues.
The kidnappers claimed to have infiltrated a marine outpost, lured Cpl Hassoun outside and abducted him. Al-Jazeera television said the militants demanded the release of all Iraqis "in occupation jails" or the hostage would be killed.
They identified themselves as part of Islamic Response, the security wing of the National Islamic Resistance 1920 Revolution Brigades.
The group first surfaced in an August 12 statement claiming the US was hiding its casualty tolls in Iraq to help US President George W Bush's election chances.
More than 40 people have been abducted in Iraq since April, many of them released or freed by the coalition. But three have been killed an American and a South Korean, who were beheaded, and an Italian.
Cpl Hassoun's family in the Salt Lake City, Utah, asked people to join them in prayers.
"We accept destiny with its good and bad," Hassoun family spokesman Tarek Nosseir said in a brief statement Sunday. "We pray and plead for his safe release."
Death threats against hostages as well as insurgent attacks accelerated ahead of Iraq's return to self-rule yesterday.
The transfer of sovereignty had been scheduled for tomorrow but the US-led coalition sped up the move by two days in an apparent bid to head off any attempts at sabotage.
Earlier Sunday, the kidnapped Pakistani driver was shown on a tape broadcast by Al-Arabiya TV. The hostage displayed an ID card issued by the US firm Kellogg, Brown & Root, a subsidiary of Halliburton.
Four masked men holding assault rifles said they would behead the Pakistani within three days unless Americans freed prisoners held at Abu Ghraib and at the cities of Balad, Dujail and Samarra.
In Istanbul, Turkish Defence Minister Vecdi Gonul rejected demands by Abu Musab al-Zarqawi's group for Turkish companies to quit doing business with US troops in Iraq to spare the lives of the three Turkish hostages. "Turkey will not bow to pressure from terrorists," Mr Gonul said.