Michel Aoun, leader of Lebanon's National Patriotic Movement, has been holding meetings with Syrian officials after arriving in Damascus.
He said just before departing for Syria on Wednesday that his visit to Syria is justified now that diplomatic ties have been set up between Damascus and Beirut.
"They are welcoming me with admiration and respect ... I was a rival and the rivalry has ended and I may become a friend," he said.
Aoun said he saw no reason not to go to Syria given that Damsacus withdrew its troops from Lebanon in 2005 and that diplomatic ties between both countries were officially launched in October.
"This is a friendly and introductory visit," he said.
Under fire
Aoun's move has come under fire from members of the ruling March 14 coalition, who accuse him of being a turncoat and of kowtowing to his former adversaries for political gain.
A former army chief, Aoun, 73, was forced into exile after being defeated in a Syrian offensive in 1990 at the end of Lebanon's 15-year civil war.
He had declared a "war of liberation" against enemy forces.
Aoun returned in May 2005, a month after Damascus ended 29 years of military domination in the aftermath of Rafiq al-Hariri, the assassination of former Lebanese prime minister.
He said his Lebanese foes would do better to clean up their own act rather than pointing fingers.
"In my talks ... tomorrow [today] in Syria or yesterday in Iran or any country in the world ... the issue will be Lebanon, not Michel Aoun," he said.
Tense relations
Aoun stunned Lebanon in 2006 when he entered an alliance with Hezbollah, the Shia group backed by Iran and Syria, a move that is thought to have caused his popularity to slip.
Syria and Lebanon launched diplomatic ties for the first time in October after years of tense relations following al-Hariri's murder.
Syria was widely blamed for the killing but denies involvement.
Aoun also caused a stir when he visited Iran in October and held talks with Mahmoud Ahmadinejad, the Iranian president.
PHOTO CAPTION
Lebanon's Christian opposition leader Michel Aoun smiles during a press conference in Beirut, ahead of his planned visit this week to Damascus.
Al-Jazeera