The oil-rich Gulf kingdom, until recently Beirut's main source of funding for arms, has cut off supplies in protest at Hezbollah's influence there.
Saudi Arabia sees the Iranian-backed Lebanese militia movement as a threat and has blocked $4 billion in military aid and urged its citizens to leave Lebanon.
Like Riyadh, Washington regards Hezbollah as a terror group. On Tuesday US officials said supporting the Lebanese army would dilute the militia's influence.
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"We believe that the Lebanese armed forces deserve the support of the international community," State Department spokesman John Kirby said.
"Assistance to the Lebanese armed forces and to other legitimate state institutions is essential to help diminish the role of Hezbollah and its foreign patrons," he said, in an implicit swipe at Iran.
"We've raised our concerns about the reports of aid cut off with the Saudi authorities. I'm not going to talk about the details of that."
Over the weekend, Saudi Foreign Minister Adel al-Jubeir said the kingdom would honor a $3 billion contract with France to buy arms for Lebanon, but would then keep the weapons for itself and not pass them on.