Mr Harari said the claim reminded him of similar ones against Iraq
The Lebanese prime minister has denied allegations that militant group Hezbollah has been supplied with Scud missiles by neighbouring Syria.
Saad Hariri said the accusation, made by Israel, reminded him of the false claim that Iraq had weapons of mass destruction.
The Western-backed Mr Hariri is in a coalition government with Hezbollah, the militant Shia Muslim organisation.
Hezbollah fought a 34-day conflict with Israel in 2006.
"Threats that Lebanon now has huge missiles are similar to what they used to say about weapons of mass destruction in Iraq," Mr Hariri said.
The US last week summoned Syria's most senior diplomat to review its "provocative behaviour" concerning the alleged transfer of weapons to Hezbollah.
Israel's President Shimon Peres accused Damascus of supplying long-range Scud missiles, which could hit anywhere in Israel.
The missiles are capable of carrying a warhead weighing up to a tonne.
In the 2006 Hezbollah-Israel conflict, more than 1,200 Lebanese people, mostly civilians, were killed. Some 160 Israeli people, most of whom were soldiers, also died.
UN Security Council resolution 1701, which ended the conflict, included an arms embargo on Lebanon, except for transfers authorised by the Lebanese government or UN.
But many analysts believe Hezbollah has since been rebuilding its arsenal with the help of its backers, Syria and Iran.
Meanwhile, Syrian President Bashar al-Assad could be about to travel to Egypt to meet President Hosni Mubarak and Saudi Arabia's King Abdullah, according to reports in the Egyptian capital Cairo.
The three-way summit has not been confirmed.
It would be the first time that Mr Assad has been to Egypt since the 2006 conflict, says the BBC's Christian Fraser in Cairo.