A fuller inquiry may be needed into the assassination of former Lebanese PM Rafik Hariri, UN chief Kofi Annan has told the Arab summit in Algiers.
The UN secretary general is one of a number of international guests
Mr Annan said he would be publishing initial UN findings into Mr Hariri's death within the next few days.
He also said he expected the withdrawal of all Syrian troops and security personnel from Lebanon before parliamentary elections next month.
He insisted the elections must be free and fair and take place as scheduled.
The Lebanese opposition is demanding a full international investigation into the bombing, saying they do not trust the pro-Syrian security chiefs in Lebanon.
Opposition figures and huge protest rallies have accused Syria and its client government in Beirut of complicity in the killing of the popular former prime minister.
Syria has denied the accusation.
The Lebanese government says it is holding its own investigation into the explosion but has not made any official statements.
The meeting in Algiers - which marks 60 years of the Arab League - has sidestepped formal discussion about the Lebanon crisis, apart from an expression of support for Syria.
"[Hariri's] vicious assassination... was a severe blow," Mr Annan told the meeting. "He was a Lebanese patriot, a formidable statesman and a vital presence in the international community."
Saudi Middle East peace plan
Expression of support for Syria
Pan-Arab "parliament" to discuss political reform
An Irish-led investigation has spent three weeks inspecting the scene of the assassination and meeting Lebanese politicians, security and judicial officials, as well as members of the opposition.
"A more comprehensive investigation may well also be necessary," Mr Annan said
Mr Annan said he was encouraged by a pledge from Syrian President Bashar Assad in a meeting Tuesday that he would "fully and completely" implement UN Resolution 1559 calling for troops to leave.
Immediately afterwards, Libyan leader Muammar Gaddafi - a past master at upstaging Arab League gatherings - defended Syria in a long off-the-cuff speech that often drew laughs from other delegates.
"Is Syria the only country in the world with an army outside its own?" he asked, referring to the US military presence in Iraq.
"Is 1559 the only sacred resolution in the UN?" he asked, suggesting that only UN resolutions against the Arabs were seen as binding, while those against Israel were not.
He also described Israelis and Palestinians as "idiots" - the Israelis for neglecting the West Bank for 20 years after they established a state, and the Palestinians for failing to establish a state during that time.
Meanwhile, on the sidelines of the summit Moroccan King Mohammed VI and Algerian President Abdelaziz Bouteflika held a rare round of talks which Algerian officials called "very cordial and fruitful".
It was King Mohammed's first visit since ascending the throne in 1999.