The vice president also underscored "the commitment of the United States to supporting the development of strong and effective Lebanese state institutions," it added.
Hariri is faced with a difficult choice over the UN's Special Tribunal for Lebanon, whose pursuit of his father's assassins could wreak havoc on his country.
Pro-Saudi billionaire and former prime minister Rafiq Hariri was assassinated in a massive car bombing in Beirut that also killed another 22 people.
The UN tribunal has said it will issue indictments "very soon."
But backed by Syria and Iran, the Shiite militant group Hezbollah, the most powerful armed movement in Lebanon, says its members are about to be fingered by the tribunal, which was set up in 2007.
Hezbollah fought a devastating 2006 war with Israel, and has warned any such accusation would have grave repercussions in Lebanon accusing the probe of being an Israeli-American plot.
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