BAGHDAD, Iraq – A posting on an Islamic Web site claimed yesterday that the Al Qaeda-linked group led by Abu Musab al-Zarqawi has slain an American hostage in Iraq, just 24 hours after grisly video showed the terror mastermind beheading another American captive.

The posting was followed about two hours later by a claim on a different Web site threatening to kill a third hostage, a British man, if women prisoners in Iraq are not freed. Neither claim could immediately be verified.

Mr. al-Zarqawi’s group, Tawhid and Jihad, kidnapped two Americans – Jack Hensley and Eugene Armstrong – and Briton Kenneth Bigley on Thursday from a home that the three civil engineers shared in an upscale Baghdad neighborhood. Mr. al-Zarqawi beheaded Armstrong, and the terrorists on Monday posted a gruesome video of the 52-year-old man’s death.

The new postings followed the passing of the terrorists’ 24-hour deadline for the release of all Iraqi women from prison, and after anguished relatives in America and Britain begged for the lives of Bigley, 62, and Hensley, who would have marked his 49th birthday today.

“The nation’s zealous sons slaughtered the second American hostage after the end of the deadline,” the first statement said. It was signed with the pseudonym Abu Maysara al-Iraqi, the name usually used on statements from Mr. al-Zarqawi’s group. Claims on this Web site have proven to be accurate in the past. The brief statement did not give the name of the hostage killed. It promised video proof soon.

Tawhid and Jihad – Arabic for “Monotheism and Holy War” – has claimed responsibility for killing at least seven hostages, including another American, Nicholas Berg, who was abducted in April. The group has also said it is behind a number of bombings and gun attacks.

This week’s back-to-back killings represented a heightened level of psychological warfare in Mr. al-Zarqawi’s campaign of terror.

A host of terrorist groups have used kidnappings and bombings as their signature weapons in a blood-soaked campaign to undermine interim Prime Minister Allawi’s government and force America and its allies out of Iraq. The violence has already persuaded companies to leave Iraq, hindered foreign investment, led firms to drop out of aid projects, restricted activities to relatively safe areas, and forced major expenditures on security.

A car bomb wounded four American soldiers on the road to Baghdad’s airport and two Marines were reported killed in separate attacks west of the capital, underscoring the inability of American forces to control key areas of Iraq 17 months after starting operations here.

Mr. al-Zarqawi, standing alongside four other masked terrorists clad in black, personally cut off Armstrong’s head, the CIA confirmed after analyzing his voice on Monday’s footage.

Armstrong’s body was discovered only blocks from where he lived, officials and witnesses said.

Rick Gamber, Armstrong’s cousin, told NBC’s “Today Show” that the family doesn’t want revenge.

“Our family feels a great deal of grief,” he said. “We hope the criminals are brought to justice, but we certainly don’t want people to overreact and do something foolish.”

Meanwhile, a Turkish construction company announced yesterday that it was halting operations in Iraq in a bid to save the lives of 10 employees kidnapped by terrorists.

Meanwhile, state TRT TV reported the body of a Turk, identified as Akar Besir, was found early yesterday near the northern Iraqi city of Mosul. The report said Besir was employed as a driver for a firm working for the American military and was kidnapped on Saturday.

Also yesterday, Tahsin Top, a Turkish hostage in Iraq whose company withdrew from Iraq was released by his kidnappers, the Foreign Ministry said.