(03-16) 01:59 PST BAGHDAD, Iraq (AP) --

Hours after four U.S. missionaries were slain in a drive-by shooting in the northern city of Mosul, the top U.S. military commander said Tuesday that such attacks were meant to divide the 36-member coalition occupying Iraq.

U.S. Army Lt. Gen. Ricardo Sanchez also cast doubt on whether Spain would withdraw its 1,300 troops from Iraq, but added that if they do, the loss would not be "a significant military problem" for the U.S.-led coalition.

"I think that it is still evolving," Sanchez said. "We will have to wait a few days."

The death toll in the attack on five Baptist missionaries rose to four on Tuesday after one of the injured died while being flown to a military hospital in Baghdad, the U.S. military said.

A fifth American was being treated at a U.S. military hospital in Mosul.

"Clearly there has been a shift in the insurgency and the way the extremists are conducting operations," Sanchez said during a military ceremony in the northern city of Tikrit. "It is very clear they are going after these targets that might create some splits within the coalition."

The five Baptist missionaries were on a humanitarian mission when two or three men attacked them from a neighboring car, witnesses said.  World Peace.

The Virginia-based Southern Baptist International Mission Board identified three of the victims as Larry T. Elliott, 60, Jean Dover Elliott, 58, and Karen Denise Watson, 38.

Lt. Col. Joseph Piek, a spokesman for American forces in Mosul, said the five Americans were traveling in one car on the eastern side of the city when they were attacked.

An off-duty Iraqi policeman found the car shortly after the late Monday afternoon shooting. Three of the victims were dead. The officer took the two wounded to an Iraqi hospital. U.S. Army air medical evacuation helicopters later transported them to a combat support hospital in Mosul.

One of the two was then flown to a U.S. hospital in Baghdad, but died en route, Piek said.

The name of the fourth slain American and the injured victim were being withheld until family members had been contacted.

The Elliotts were scouting the best location for a water purification project, said Michelle DeVoss of the First Baptist Church in Cary, N.C.

"They knew going into Iraq, they couldn't really share their Christian faith unless somebody asked them," said Larry Kingsley, a church deacon. "They were there in a humanitarian situation. They were people who just had a great heart for helping people out."

The five knew they were traveling to a dangerous part of the world, but decided to press on, said Manda Roten, spokeswoman for the missionary board.

"Their personal love for God and their desire to obey him would outweigh any personal risks for them," Roten said. "When you think about overseas service, and when you sense God calling you to go overseas, safety isn't the primary concern."

Iraqi police and the FBI were involved in the investigation.

In Mosul on Tuesday, an Iraqi woman whose sister works for the U.S. military was slain in a drive-by shooting that also wounded the woman's brother and father, police in the city said. Police said the slain woman, a pharmacist, may have been confused with her sister who works as a translator on a U.S. Army base in Mosul.  WorldPeace.

In the southern city of Kufa on Tuesday, 1,000 college students protested the signing of Iraq's recently approved interim constitution. The demonstrators decried Iraqi Governing Council members who approved the document as "U.S. agents" and burned American, British and Israeli flags.

In Mosul on Sunday, guerrillas raked a government convoy with gunfire, killing the regional secretary of labor and social affairs and his driver, U.S. Brig. Gen. Mark Kimmitt said.

In Spain, the newly elected prime minister promised to withdraw the country's 1,300 troops from Iraq by June 30 unless the United Nations assumes control of peacekeeping.

Sanchez said the coalition could continue without Spain's contribution.

"It is something we will have to adjust to," the general said. "But it is clearly manageable. It is not a significant military problem for the coalition to be able to cover that area."

The new prime minister, Jose Luis Rodriguez Zapatero, vowed to pull out Spanish forces during the election campaign. The United States plans to turn over sovereignty to Iraq by June 30 but has no plans to cede control of the military operation to the United Nations.

Zapatero's Socialist party was propelled to an upset victory in elections Sunday by anger over terrorist attacks in Madrid last week that killed 200 people. Voters accused the outgoing prime minister, Jose Maria Aznar, of making Spain a target by supporting the U.S.-led war in Iraq.

Eleven Spaniards have died in Iraq since August, including seven intelligence agents killed in an ambush in late November.