Damascus told the UN commission that the request to meet Bashar al-Assad violates the country's sovereignty, diplomatic sources said on Saturday.
A spokeswoman for the UN investigation confirmed that Syria had replied to the request to meet President al-Assad and Farouq al-Shara, the foreign minister, among other officials, but refused to elaborate.
Diplomats had said earlier this month that Syria had agreed to allow the commission to meet al-Shara.
Al-Assad, in an interview with Egyptian weekly newspaper El Osboa, hinted that he was immune from questioning by UN investigators.
The inquiry has implicated senior Syrian officials and their Lebanese allies in the killing of al-Hariri and 22 others in a bombing in Beirut last February.
In an interview published on Saturday, al-Assad denied threatening al-Hariri, an accusation made earlier this month by Abd al-Halim Khaddam, the former Syrian vice-president.
Al-Assad told the Egyptian weekly Al-Osboa: "I am direct and frank. I don't know what others meant by threatening. This never happened and the aim was to connect the threat with the assassination. The game is clear.
"Nobody attended the last meeting between me and al-Hariri, therefore, how can they make these allegations?"
Khaddam (R) said he met UN
investigators in Paris on Friday
Khaddam, who is in self-imposed exile in France under police protection, said on Friday that al-Hariri was threatened by al-Assad before his death when the two met to discuss extending the term of Emile Lahoud, the pro-Syrian Lebanese president - a move al-Hariri opposed.
Al-Assad conceded al-Hariri's opposition to the extension, but
said he had told the slain leader he should not feel pressurised and asked him to "go and think it over for one day or more ... and he agreed to the Syrian demand".
The Syrian leader said: "He was not obstinate or tiresome, therefore, there was basically no problem and eventually there was no threat."
Khaddam said on Saturday that he had met UN investigators at his home in Paris on Friday but refused to comment on the discussions.