BEIRUT—Thirteen French tanks, the most powerful armour ever deployed by a United Nations peacekeeping force, rolled ashore yesterday, beefing up a mission aimed at helping cement an uneasy ceasefire in Lebanon.

But some European officials are concerned international peacekeepers will be at best ineffective and at worst humiliated if hostilities flare between Hezbollah fighters and Israeli troops.

Scores of blue-helmeted French troops transferred the Leclerc tanks, AUF-1 artillery cannons, two high-tech Cobra radar trucks and dozens of armoured vehicles and transport trucks from a cargo ship in Beirut's port. The port reopened Friday after a nearly two-month Israeli blockade.