United Nations officials confirm at least three Syrians were killed and 16 others injured on Sunday when their bus was hit by a stray missile as it traveled inside Iraq toward the Syrian border.

David Wimhurst of the U.N. Coordinating office in Jordan said the Syrians were traveling in a convoy of 16 vehicles near the Iraqi town of Rutbah when the missile hit.

Mr. Wimhurst said the U.N. has once again appealed to all sides to protect civilians caught in the conflict. "This deadly event underlines again the enormous responsibility combatant forces bear regarding the security and safety of civilians," he said.

U.N. officials are also warning of a health hazard because of disruption in water supplies in the southern city of Basra.

UNICEF spokesman Geoffrey Keele said there is an urgent need for drinking water in the city. He said power cuts are interrupting distribution from a water plant that supplies 40 percent of Basra's population.

"There must now be a threat as tens of thousands of people in their homes, hospitals and care institutions attempt to cope and find what water they can from the river and other sources," Mr. Keele said.

Mr. Keele said insufficient supplies of clean drinking water pose a health risk, particularly for young people. "Bad water cost lives, especially for the most vulnerable. And the children of Iraq are certainly among the most vulnerable people in the world," he said.

The UNICEF spokesman estimates that 100,000 Iraqi children under the age of five are susceptible to dehydration and diarrhea.

He said U.N. teams are monitoring the situation in Basra from across the nearby Iranian border and will try to provide clean drinking water as soon as it is safe to move into the city. For now, teams from the International Red Cross in Iraq have managed to restore some of the Basra plant's water pumping operation.