Later in Saudi Arabia, Francois Hollande held further talks on Syria with King Abdullah, whose country has been a leading supporter of the forces trying to overthrow Syria's President Bashar Assad.
In Beirut, Hollande promised that Paris and the European Union will help Lebanon deal with an influx of more than 100,000 refugees who have fled the civil war in neighboring Syria.
"We are committed to give you guarantees regarding security, stability and unity of Lebanon," Hollande told reporters after meeting President Michel Suleiman.
The Oct. 19 car bomb that killed Brig. Gen. Wissam al-Hassan, a powerful anti-Syrian intelligence official, stirred up deadly sectarian tensions in Lebanon, where Sunnis and Shiites are deeply divided over the civil war in Syria, which has killed at least 36,000 people since it began in March 2011.
Lebanon's two largest political coalitions have lined up on opposite sides of the conflict. The powerful Shiite group Hezbollah and its partners who dominate the Lebanese government have stood by Assad, while Lebanon's Sunni-led opposition backs the rebels seeking to topple the Damascus regime.
Assad and many in his inner circle are Alawites—an offshoot of Shiite Islam and a minority in Syria—while the rebels come mostly from the country's Sunni majority.
Syria dominated Lebanon for 29 years after it first sent troops into its smaller neighbor in 1976, during Lebanon's 15-year civil war.
Damascus' three-decade hold on Lebanon began to slip in 2005, after the assassination of former Lebanese Prime Minister Rafik Hariri. Still, for years after Syrian troops pulled out, there were frequent assassinations of anti-Syrian figures in Lebanon, and the perpetrators have yet to be tracked down.
Despite the Syrian military's withdrawal from Lebanon, Assad has managed to maintain his influence in the country through allies, such as Hezbollah.
Hollande made a three-hour stop in Beirut en route to Saudi Arabia for talks that focused on the Syria conflict and Iran's disputed nuclear program. Saudi officials said Hollande arrived in the Red Sea port of Jiddah, accompanied by a high-level delegation that included French Foreign Minister Laurent Fabius and a senior trade official.
France's ambassador to Saudi Arabia said in comments published in the Al-Riyadh newspaper Sunday that Paris and Riyadh share views on both issues. The newspaper quoted Bertrand Besancenot as saying France backs tighter sanctions on Iran and calls on Syrian President Bashar Assad to step down.
Saudi Arabia is Iran's main regional rival and is a key backer of Syria's rebels.
While in Beirut, Hollande said France will give "full assistance" in the investigation of al-Hassan's assassination, saying "the Lebanese and the world want this. There will be no escape from justice."
Al-Hassan was killed a day after he returned home from Paris, where his family has been living for years.
"Even though Lebanon is very close, it should not be the victim of this crisis," Hollande said referring to Syria's civil war. "We renew France's full support to the stability, unity, independence and safety of the territory of Lebanon."
France, the onetime colonial ruler of both Syria and Lebanon, has been one of the most outspoken Western critics of the Assad regime. France announced in September that it had begun sending direct aid and money to five rebel-held Syrian cities as part of its intensified efforts to weaken Assad. It was the first such move by a Western power amid mounting calls for the international community to do more to prevent bloodshed.
French officials have acknowledged providing communications and other non-lethal equipment to Syrian rebel forces, but say they won't provide weapons without international agreement. Paris played a leading role in the international campaign against Libyan dictator Moammar Gadhafi last year.
France still wields wide influence in Lebanon and has about 900 peacekeepers deployed near the border with Israel.