Iraq's top Shiite Muslim cleric on Monday condemned as "hideous crimes" the coordinated bomb attacks on five churches in Baghdad and Mosul that killed at least seven people and marked the insurgency's first major attacks on Iraq's minority Christians.

Masked gunmen killed a Turkish hostage with three gunshots to the head, according to a video posted on the Internet Monday, and the Turkish truckers' union said it would stop bringing supplies to U.S. forces in Iraq, bowing to militant demands in hopes of saving two other captive Turks.

Grand Ayatollah Ali al-Husseini al-Sistani (search) said in a statement that Sunday's assaults on churches "targeted Iraq's unity, stability and independence."

The unprecedented attacks against Iraq's 750,000-member Christian community appeared to confirm Christians' fears of being targeted as suspected collaborators with American forces amid a rising tide of Islamic fundamentalism.

"We hope this cloud of fear will go away," said Father Faris Thomas of St. Peter's Seminary in Baghdad, one of the targeted churches. "We try and tell [our people] that everything will be OK, but now that something has happened, it's changed everything."

The church bombings signaled a change in tactics for insurgents, who have focused previous attacks on U.S. forces, Iraqi officials and police, and foreign workers. The murder of the Turkish hostage was the latest bloodshed in an insurgent campaign aimed at forcing coalition forces out of Iraq and scaring foreign companies from operating here.

Several nations — most recently the Philippines — have withdrawn troops from Iraq in the increasing militant violence, and several companies have met militant demands to spare employees. The same group that claimed to have killed the Turk said Monday it would free a Somali captive because his Kuwaiti employer agreed to cease business in Iraq.

In the videotape, posted on an Islamic Web site used by militant groups, a man kneels in front of three armed men and reads a statement in Turkish. He identifies himself as Murat Yuce from the Turkish capital, Ankara, an employee of a Turkish company that subcontracted for a Jordanian firm.

"I have a word of advice for any Turk who wants to come to Iraq to work: 'You don't have to be holding a gun to be aiding the occupationist United States. ... Turkish companies should withdraw from Iraq," he says.

At the end of the statement, one of the masked men takes out a pistol and shoots the Turk in the side of the head. He slumps to the ground, and the kidnapper shoots him in the head twice more. Blood is seen on the ground next to his head.

A black banner on the wall identifies the group as Tawhid and Jihad (search). The group — led by the Jordanian militant linked to Al Qaeda, Abu Musab al-Zarqawi (search) — kidnapped two other Turks last week, both truck drivers.

In Ankara, Yuce's employer, Bilintur, issued a statement saying it had heard of his killing. It said he was one of two employees missing in Iraq for three or four days.

"Our grief is huge," it said.

It said Bilintur was providing a laundry service for a Jordanian company in Iraq. It did not identify the other missing employee.

The head of Turkey's International Transportation Association, Cahit Soysal, said Monday that by agreeing to stop working with U.S. forces in Iraq, Turkish truckers hope the kidnappers will release the two drivers.

Soysal said the stoppage would affect only the 200-300 trucks owned by more than a dozen Turkish companies that had brought supplies — mostly fuel — to U.S. forces every day. Another 1,700-1,800 trucks with supplies for other purposes would continue to cross the border into Iraq, he said.

Many of the more than 70 foreigners abducted by militants have been truck drivers, more vulnerable to attack than heavily armed troops.

In a separate video, broadcast on the Arab station al-Jazeera, Al-Zarqawi's group said it would release a Somali truck driver it kidnapped because his Kuwaiti employer agreed to stop working in Iraq.

Tawhid and Jihad had threatened July 29 to behead Ali Ahmed Moussa within 48 hours if his company failed to leave. It was not known when he was kidnapped.

In the video aired Monday, Moussa kneels before three black-clad, masked gunmen. One of the militants says the group is releasing Moussa "in appreciation of the attitudes of the Somali government and people toward Iraq and the Kuwaiti company's commitment to stop doing business in Iraq."

There was no word on when the Somali would be released, and his Kuwaiti employer has not been publicly identified.

Tawhid and Jihad has claimed a number of bloody attacks across Iraq and, since April, the beheadings of several foreigners including U.S. businessman Nicholas Berg (search), South Korean translator Kim Sun-il (search) and Bulgarian truck driver Georgi Lazov (search).

On Sunday, Iraqi gunmen released one of two Lebanese businessmen, a day after they were snatched on a Baghdad street. The fate of the other hostage is unknown.

No group claimed responsibility for the Christian church attacks, though Deputy Prime Minister Barham Saleh said, "Sources of danger ... are represented by Al Qaeda's followers and supporters of the former [Saddam Hussein] regime."

The wave of explosions — at least four of them car bombings — began after 6 p.m. Sunday as parishioners gathered for services and came just minutes apart. They hit four churches in Baghdad and a fifth in Mosul, about 220 miles north of the capital. The attacks did not appear to be suicide bombings, U.S. military and Iraqi officials said.

The Baghdad attacks killed five people and wounded 29, and the Mosul blast killed two and injured eight, the Iraqi Health Ministry said. The U.S. military had a different count of 10 killed in Baghdad and one in Mosul.

The attacks could have been worse. On Monday, Baghdad residents found a bomb in a trash pile outside one of the churches targeted Sunday, the third unexploded bomb found near a church in less than a day.

Despite the attack, Iraq stands united, said Roman Catholic Chaldean Patriarch, the Rev. Emmanuel Delly.

"Perhaps they wanted to divide us from our Muslim brothers, but we and the Muslims are one family — one Iraqi family that should be protected by brotherhood and love," he said.

Pope John Paul II sent Delly a condolence telegram.

"The sorrowful news ... against various Catholic communities gathered in prayer in their houses of worship struck me deeply," the pope said.

Muslim clerics condemned the violence and also offered condolences to Iraq's dwindling Christian community. Many Christians have already fled to neighboring Jordan and Syria to escape violence in the insurgency-wracked nation.

"This is a cowardly act and targets all Iraqis," Abdul Hadi al-Daraji, spokesman for radical Shiite cleric Muqtada al-Sadr (search), told Al-Jazeera television.

The more senior al-Sistani, based in the southern city of Najaf, said: "We assert the importance of respecting the rights of Christian civilians and other religious minorities and reaffirm their right to live in their home country Iraq in security and peace."