Dominique de Villepin landed in Beirut on Monday afternoon and went straight into talks with the Lebanese prime minister, Fuad Siniora, officials said.
Philippe Douste-Blazy, France's foreign minister, accompanied him.
De Villepin called for "an immediate humanitarian truce" to end the hostilities between Israel and the Lebanese Shia group Hezbollah.
Jacques Chirac, the French president, dispatched his prime minister and foreign minister to meet Siniora and "convey to him the support of France and the solidarity of the French people with the Lebanese people in their ordeal," the president's office said.
At the close of the G8 summit on Monday, Chirac said that returning stability to Lebanon may require "means of coercion."
"Some kind of buffer zone is needed; the idea is to have an international force and a line of surveillance" in southern Lebanon.
"We have a situation that requires outside intervention, in such a way as to assure borders and to avoid cross-border aggression by one side against the other"
the French president
A day earlier, leaders at the G8 summit adopted a statement blaming Hezbollah for escalating the violence, and recognising Israel's right to defend itself, though it called on the Jewish state to show restraint.
France's move to throw support behind Lebanon was not a sign of disagreement among the G8 leaders, said the foreign policy aide of the Russian president.
"The statement on the Middle East (reflected) the collective position of the G8," Sergei Prikhodko said.
"We proceeded from the fact that France feels special responsibility, having special relations ... with Lebanon and considers this step important and necessary," he said.
Asked about the implementation of a September 2004 UN Security Council resolution that calls for disarming militias in Lebanon, the French president said: "This will probably demand some means of coercion.
"Things cannot go on like this," Chirac said. "A means for repression, when needed, and in any event for surveillance, is required.
"We have a situation that requires outside intervention, in such a way as to assure borders and to avoid cross-border aggression by one side against the other."
Chirac's comment came a day after leaders of the world's eight most industrialised nations proposed the deployment of an international force in south Lebanon to help stem fighting between Israel and militant groups.
France hopes to evacuate 1,250 people, some of them nationals of other Western countries, on board a ferry which docked at the port of Beirut on Monday, the foreign ministry said in Paris.
The two countries have historic ties: France ruled Lebanon through a League of Nations mandate from the end of World War I until independence in 1943.
Lebanon is proud of its French heritage and promotes it, and many Lebanese still send their children to French schools.