"I am shocked and deeply distressed by the apparently deliberate targeting by Israeli Defense Forces of a U.N. Observer post in southern Lebanon," Annan said Tuesday in a statement made in Rome, where he is to attend a high-level international meeting on Lebanon on Wednesday.
He called the act a "coordinated artillery and aerial attack on a long-established and clearly marked U.N. post," and said he had received "personal assurances" from Israeli Prime Minister Ehud Olmert that United Nations' positions would be spared.
Annan said General Alain Pelligrini, the U.N. force commander in south Lebanon, had been in regular contact with Israeli officers throughout the day Tuesday, and had stressed the need "to protect that particular U.N. position from attack."
"I call on the government of Israel to conduct a full investigation into this very disturbing incident and demand that any further attack on U.N. positions and personnel must stop," Annan said.
The names and nationalities of those killed are being withheld until family members can be notified.
The news of the deaths came as the U.N. Security Council discussed the future of the U.N. Interim Force in Lebanon. The mandate ends at the end of the month, and Lebanon has asked for a six-month extension.