"Russia is shocked by the tragedy and expresses its sincere condolences" to the governments involved and the families of the victims, the Foreign Ministry said in a statement.

Four UN observers from Austria, Canada, China and Finland were killed in an Israeli airstrike on a UN post in southern Lebanon on Tuesday.

UN Secretary General Kofi Annan, who said the attack was "apparently deliberate," on Wednesday called for a joint investigation with Israel into the killing of the four peacekeepers.

"Attacks at peacekeepers cannot be justified and are unacceptable," the ministry said. The incident shows again the need for an immediate ceasefire in the region, it added.

"The UN Security Council should not stand aside when the lives of UN peacekeepers are at risk," the statement said. All countries concerned should make joint efforts based on UN resolutions to find a solution acceptable to all, it said.