"Ending the era of impunity for political assassinations is essential to realizing the justice and stability that the Lebanese people deserve, and any attempt to interfere with the Tribunal's work or fuel tensions within Lebanon must not be tolerated," Obama said in a statement issued on the eve of the sixth anniversary of the car bombing that killed Hariri and 22 others. "The cause for which Prime Minister Hariri and so many Lebanese patriots gave their lives must remain our guide."
The U.N.-backed tribunal is widely expected to accuse Hezbollah members of involvement in the 2005 killing. The Shiite militant group and its allies walked out of the previous government after then-Prime Minister Saad Hariri - the slain man's son - refused to denounce the tribunal.
Hezbollah may be in a position to block the court's work after its favored candidate, Najib Mikati, was named Lebanon's new prime minister.
"This is a decisive moment for Lebanon," Clinton said in separate statement on Sunday. "Those who would try to block Lebanon's cooperation should desist and show a measure of human decency. Ultimately, without justice, there can be no peace and stability for Lebanon."