A bomb has hit a UN convoy near the southern Lebanese city of Sidon, wounding six Italian peacemakers, officials say.
Italian military spokesman Massimo Fogari said two soldiers were in a serious condition. Earlier reports said one peacekeeper had died.
A spokesman for the UN Interim Force in Lebanon (Unifil) told Reuters the bomb had been aimed at a logistics convoy.
Unifil is tasked with keeping peace in the tense border region with Israel.
Images from the scene show a large hole blasted through a concrete safety barrier on the side of the road.
Italian Foreign Minister Franco Frattini expressed "sorrow" for the victims.
He praised the Unifil mission, saying it made a "decisive contribution to the stability of one of the most sensitive Middle Eastern areas".
Lebanese Prime Minister-designate Najib Mikati condemned the blast in a phone call to the UN special co-ordinator for Lebanon, Michael Williams.
So far no group has said it carried out the attack.
The last such attack on Unifil was in January 2008 when a roadside bomb hit a UN vehicle south of Beirut, wounding two peacekeepers.
In June 2007, six Spanish peacekeepers died when a bomb hit their armoured personnel carrier near the Israeli border.
Unifil has about 13,000 troops stationed in the south of Lebanon, with Italy providing the largest contingent.
It was formed in 1978 after Israeli troops entered southern Lebanon and began a 22-year occupation.
The force was expanded after the 2006 war between Israel and the Lebanese militant group Hezbollah.