The gunmen swarmed the bus as it pulled up to the Bakhan Hotel at dawn to pick up the man, identified by police as Abdulkadir Tanrikulu. The gunmen opened fire, killing the bus driver and five of Tanrikulu's employees, police said. The attackers then sped off with their captive.
It was the latest bloodshed in a surge of violence about two weeks before Iraqis will choose a national legislature in the first election since the collapse of Saddam Hussein's government.
In a followup attack in the Shiite area, a suicide car bomber attacked a Shiite Muslim community center Thursday, killing three people and wounding eight, police said.
The community center attack occurred in Khan Bani Saad, a market town 18 miles north of the capital Baghdad, about 8 p.m. in front of the Shiite center, said police warrant officer, Jassim Abbas.
In other developments:
The slaying of the cleric's representative was apparently meant as a warning to al-Sistani, who strongly backs the Jan. 30 vote. Rebels have also targeted electoral workers and candidates.
Shiites make up 60 percent of Iraq's 26 million people and are expected to dominate the 275-member National Assembly. Many Sunnis, who make up 20 percent of the population, fear a loss of the influence and privilege they enjoyed for decades. And Sunni clerics have called for a boycott to protest the November assault on the insurgent stronghold of Fallujah.
U.S. and Iraqi officials fear that a low Sunni turnout will cast doubts on the new government's legitimacy.
Al-Sistani has urged Iraqis to vote, calling it a religious duty for every man and woman. The Iranian-born cleric is not running himself but is backing the 228 candidates from the United Iraqi Alliance, a coalition of 16 groups that includes Iraq's largest Shiite political party, the Supreme Council for the Islamic Revolution in Iraq.
If many Sunnis do stay home on election day, the United Iraqi Alliance stands to dominate the assembly.
Interim Prime Minister Ayad Allawi said Thursday that Iraqis' participation in the vote could help end the violence.
"One of the ways to end the insurgency is to continue going forward with the political process and that Iraqis participate in the political process, including elections," Allawi told Al-Arabiya television.
Also Thursday, U.S. troops clashed with insurgents in Baghdad's northern Azamiyah neighborhood, and some Iraqis were killed, witnesses said. Several cars were scorched by fire and bullet casings littered the ground. The military had no comment.
Thursday's attack at the Baghdad hotel left the pavement stained with blood. Gunmen dragged the bodies out of the minibus and drove off with it, along with the Turkish businessman.
There has been no claim of responsibility or demands.
A Turkish news channel said the man's construction company was working in Iraq with Americans. A hotel employee who gave only his first name, Alaa, said he had been in Iraq for about a year.
Nearly 180 foreigners have been taken hostage in Iraq since last April; more than 30 of them have been killed.
Also Thursday, gunmen kidnapped an Iraqi of Egyptian origin in the northern city of Kirkuk, police said. Sayyed Abdul-Khaleq was taken from the gas station he owns by gunmen dressed as Iraqi National Guard, police Maj. Gen. Torhan Abdul-Rahman Youssef said.
In another sign that insurgents were stepping up their activity in the capital, explosions rocked the area of the heavily guarded Green Zone, breaking a lull of a couple of weeks in insurgent shelling of the international district.
Two explosions were heard Thursday morning, and up to three others shook the area after sundown. It was unclear where the explosions occurred and whether there were casualties or damage.
The Green Zone, located on the western side of the Tigris River, includes major U.S. and Iraqi government offices.
Interim President Ghazi al-Yawer weighed in on the U.S. announcement Wednesday that the search for weapons of mass destruction in Iraq has concluded without finding any. President Bush had cited the weapons as justification for going to war.
Al-Yawer, in Paris for talks with French President Jacques Chirac, said the war still served a purpose.
"What has happened has happened," al-Yawer told reporters, speaking in English. "But the war rid Iraq of a vicious regime which established a dynasty of villains."