(Adds Security Council statement in paragraphs 5,6)

UNITED NATIONS, Dec 12 (Reuters) - U.N. Secretary General Ban Ki-moon condemned the assassination of a Lebanese army general on Wednesday and called for calm and restraint as the country faces a political crisis over electing a president.

A car bomb killed Brig. Gen. Francois al-Hajj, head of army operations, in a Christian suburb of Beirut, removing a leading contender to replace military chief Gen. Michel Suleiman who is set to be elected president next week.

"The Secretary-General was outraged by yet another terrorist attack in Lebanon," Ban's spokeswoman said in a statement. "The Secretary-General strongly condemns this act of violence and terror on the Lebanese Armed Forces, a symbol of Lebanon's sovereignty."

The attack heightened tension in Lebanon where rival leaders are struggling over the presidency that has fueled the biggest political crisis since the 1975-1990 civil war.

The U.N. Security Council discussed Lebanon for the second straight day and issued a statement strongly condemning the attack and stressing the importance of bringing to justice the "perpetrators, organizers and sponsors of this heinous crime."

"It underlines that no attempt to destabilize Lebanon should prevent the holding without delay of a free and fair presidential election, in conformity with Lebanese constitutional rules, without any foreign interference or influence," the statement said.

Ban's statement said this attack and previous ones aimed at undermining Lebanon's sovereignty were unacceptable.

"The Secretary General calls on the Lebanese for calm and restraint at this critical juncture in their history," it said.

"Their political leaders must exert every possible effort to resolve differences and arrive at a solution for an immediate presidential election, without conditionality, in accordance with constitutional rules." (Reporting by Claudia Parsons, editing by Chris Wilson)

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