Beirut: Senior US envoy Jeffrey Feltman on Sunday underlined Washington's firm support for a UN-backed tribunal on the 2005 murder of Lebanon's former prime minister Rafiq Hariri.

"We believe that the tribunal should be allowed to complete its work on its own timeline and without outside interference until those responsible... are brought to justice," Feltman told reporters at the Beirut airport.

"I think all of us who represent (UN) Security Council countries also understand that the work of the tribunal at this point will not be stopped," added Feltman, the US assistant secretary of state for Near Eastern affairs.

"The work of the tribunal will go on."

Feltman's statement comes growing tension in Lebanon over reports that The Hague-based tribunal is set to indict members of Syrian- and Iranian-backed Hezbollah in the assassination of Hariri, a Sunni Muslim who was close to Saudi Arabia.

The reports have raised regional fears of renewed Sunni-Shiite sectarian violence and the collapse of the politically turbulent country's hard-won national unity government.

Feltman's brief visit also coincided with talks between Saudi King Abdullah and Syrian President Bashar Al Assad in Riyadh, a meeting analysts say was to centre on the running dispute between Lebanese Prime Minister Saad Hariri, son of Rafiq, and Hezbollah over the tribunal.