An apparently different group of militants threatened to behead a Pakistani hostage if American forces do not release some prisoners being held in Iraq within the next three days.
In a declaration broadcast by the Arab language television station Al-Arabiya, three masked gunmen said the countdown began with the airing of the tape. The Pakistani hostage, who displayed an identification card issued by the U.S. firm Kellogg, Brown & Root, also appeared on the tape.
The masked men did not say whether they were affiliated with any group.
"Three days after the airing of this picture, we will cut off his head," said a stocky militant in the center of the picture whose face was cloaked by a red scarf.
The men demanded that prisoners be released from detention centers in several specific areas, including Abu Ghraib, the center of a scandal involving the abuse of Iraqi detainees by American soldiers.
The hostage, who gave his name as Amjad, urged Pakistani President Pervez Musharraf to close the Pakistani Embassy in Iraq and to ban all Pakistanis from coming to Iraq. He appealed to his countrymen not to come to work in Iraq.
The hostage insisted that his life would not be spared because he was a Muslim.
"I'm also Muslim, but despite this they didn't release me," he said. "They are going to cut the head of any person regardless of whether he is a Muslim or not."
In other violence:
The attacks came a day after a pair of car bombs hit the southern city of Hillah, killing around 20 people.
With violence persisting, security measures have been increased around government buildings, power stations and oil installations in advance of Wednesday's transfer of sovereignty to a new Iraqi administration, an official in the Interior Ministry, speaking on condition of anonymity, said. He refused to give details.
Turkey vowed that it would not negotiate with Islamic militants in Iraq who are threatening to behead three Turkish hostages. Bush said the terrorist incident would not mar a NATO summit he is attending in Istanbul.
NATO closed ranks Sunday on a pledge to help train Iraq's armed forces as violence and bloodshed surged before the delicate political turnover of formal sovereignty from the United States to Iraq on Wednesday.
Determined to offer support for the fledgling Iraqi government, NATO Secretary General Jaap de Hoop Scheffer said NATO's mission will involve alliance instructors working both inside and outside the country.
Bush's visit triggered protests by more than 40,000 Turks chanting anti-Bush slogans as they marched in the Kadikoy district, on the Asian side of Istanbul.
F-16 warplanes flew overhead while more than 23,000 police patrolled the streets.
Followers of the most wanted Islamic militant in Iraq, Abu Musab al-Zarqawi, announced Saturday they had kidnapped three Turkish workers and threatened to behead them after 72 hours unless Turkish companies stop doing business with American forces in Iraq and called for protests in Turkey against Bush's visit.
Secretary of State Colin Powell said Sunday that the United States is doing all it can to locate and free the three Turks.
"We hope it will be possible to rescue them, but it's a dangerous situation," Powell said in a broadcast interview from Turkey.
Defense Secretary Donald Rumsfeld said the United States was not planning any immediate increase in troops to deal with the insurgency as a new Iraqi government takes power this week. He noted that the number of troops had already increased over the past three to four months from 113,000 to 141,000.
"We don't want to be an occupying power," he said in a broadcast interview from Istanbul. "The Iraqi people are going to have to provide for the security of their country and they are well on the way to doing it."
Iraq's interim prime minister, Iyad Allawi, said his government wanted to try to split the insurgency by dividing less ideological members from the hardcore leaders.
"We are drawing up plans to provide amnesty to Iraqis who supported the so-called resistance without committing crimes, while isolating the hardcore elements of terrorists and criminals and undercutting their base of support," Allawi wrote in an opinion article published Sunday in Britain's The Independent newspaper.
Allawi said Saturday that violence could force the delay of national elections, a key part of U.S. efforts to bring democracy to Iraq, scheduled to take place by Jan. 31 under Iraq's interim constitution. He also said his government was drawing up a law to give security forces more power to make arrests and impose curfews.
White House spokesman Scott McClellan said the United States "remains committed" to the January timetable.
The U.S. military has posted a $10 million reward for help in capturing or killing al-Zarqawi, who is blamed for numerous bombings in Iraq and whose movement beheaded two previous hostages, an American and a South Korean.
The CIA has suspended the use of interrogation methods vetted by the White House until the completion of a review by Justice Department and other administration lawyers, intelligence officials tell The Washington Post.
The so-called "enhanced interrogation techniques" include mock drowning and refusing pain medication for injuries. The methods have reportedly been used to elicit intelligence from al Qaeda leaders such as Abu Zubaida and Khalid Sheik Mohammed.