BEIRUT (AFP) -- Arab League Secretary General Amr Mussa said that more work was needed to settle a protracted political crisis between the Lebanese government and the Syrian-backed opposition.

Mussa wrapped up a three-day mediation mission without a deal, hailing progress but urging further talks between the feuding parties over the formation of a national unity government.

"There was progress, and there is good ground for understanding, but matters demand more efforts," Mussa told reporters in the Lebanese capital.

Mussa said the Western-backed government and opposition leaders had agreed to form a new commission to discuss a controversial international tribunal into the 2005 assassination of ex-premier Rafiq Hariri, widely blamed on Syria.

A UN-proposed Hariri court "is at the top of the agenda because it is an important question linked to finding justice," Mussa said. To that end, he said parties agreed on forming "a six-member committee, including two judges and four political representatives, to examine the tribunal convention."

A UN inquiry has implicated some top Syrian figures and their Lebanese allies in the 2005 bomb blast that killed Hariri and 22 others. Syria has denied involvement.

Mussa also sketched the broad outline of what a potential new unity government would look like, and said it was among matters up for further discussion.

"The question of forming a national unity government will be examined in-depth," he said, according to a formula of 19 ministers from the anti-Syrian parliament majority, 10 ministers from the opposition and one neutral minister.