Haj, the army's operations chief, was killed by a car bomb near the presidential palace in Baabda, Middle East Newsline reported. The army said the bomb contained 35 kilograms of TNT.

"Haj was seen as the next chief of staff and he was not regarded as loyal to Syria," a Lebanese source said. "He had to go."

"The latest criminal explosion is a link in the terrorist chain directed at Lebanon and its institutions, foremost among them the national army, which today pays the price for defending Lebanon's sovereignty, independence and free will," Lebanese parliament majority leader Saad Hariri, the son of the late prime minister, said.

The area around the presidential palace was meant to be off-limits to unauthorized persons and guards. A Lebanese security source acknowledged a "momentary lapse" that allowed the car full of explosives to enter the area.

"The Syrians have penetrated Lebanese security at every level," the source said. "There's no surprise here [that the Syrians brought a car bomb near the presidential palace]."

Haj had been expected to replace Lebanese Chief of Staff Gen. Michel Suleiman, a pro-Syrian figure selected as the compromise candidate for president. Haj commanded the Lebanese Army operation against Fatah Al Islam in Naher Al Bared in May 2007. He also directed Lebanese Army deployment in the south in late 2006.

For its part, Syria has condemned the assassination. No group immediately claimed responsibility for the bombing.

"If it was a political killing, it sends a very big message to the current head of the army: Don't think that just because you're the head of the army, you're immune," Paul Salem, director of the Carnegie Middle East Center, said. "If you're going to be involved politically, don't think that you're going to be safer than politicians."