An Israeli air strike killed four United Nations military observers at their base in southern Lebanon on Tuesday, the United Nations said.

"This coordinated artillery and aerial attack on a long established and clearly marked U.N. post at Khiam occurred despite personal assurances given to me by Prime Minister Ehud Olmert that U.N. positions would be spared Israeli fire," U.N. Secretary- General Kofi Annan said in a statement issued at U.N. headquarters in New York.

Annan called on Israel to investigate the "apparently deliberate targeting" of the base.

Meanwhile, U.N. spokeswoman Marie Okabe said at U.N. headquarters in New York: "I can confirm that the four military observers that came under attack in Khiam were killed in that attack."

In Jerusalem, an Israeli army spokeswoman said the military was investigating the report.

Source: Xinhua