Lebanon's private Future Television reported that the commission's chief, German prosecutor Detlev Mehlis, would meet "a Syrian representative" in Geneva within 24 hours, citing a UN official in New York.
The UN Security Council on Thursday called on Syria to fully cooperate with the probe into the February murder of the billionaire five-time prime minister, with the United States calling Damascus's stance "unacceptable".
The council did not actually name Syria but in a statement said: "The members of the Council reiterated their call on all states and all parties, especially those who are yet to respond adequately, to cooperate fully in order to expedite the work of the (enquiry) commission."
Many in Lebanon have blamed the killing of al-Hariri on Syria and its then allies in the Lebanese government, charges vehemently denied by Damascus.
Al-Hariri's son Saad called on Syria to answer the probe's questions, saying in a statement that "countries that are brothers and friends of Lebanon are required to cooperate."
Rafiq al-Hariri was assassinated in a massive bomb blast on the Beirut seafront in February, sparking massive popular protests against alleged Syrian involvement in the killing and eventually leading to the departure of Syrian troops.
Damascus has previously said its constitution forbids its officials being questioned by foreigners.
UN Under Secretary General Ibrahim Gambari told the council on Thursday that Mehlis "has significantly advanced the course of the investigation."
"I am pleased to report that Jordan and Israel have reacted positively to the commission's requests for assistance," Gambari said.
But he said written requests for interviews and documents sent to Damascus on 19 July had not been replied to.
Gambari noted that Syria's UN envoy Faisal Mekdad had approached Mehlis through the United Nations in New York to express his country's readiness to open discussions with the commission.
But he made clear that discussions could not replace the requested assistance for the purpose of the investigation.
"Mr Mehlis is therefore of the opinion that the lack of timely response by the Syrian Aran Republic has considerably slowed down the commission's work."