Brammertz said he was "completely aware of the expectations on the part of the families of the victims, the people of Lebanon, and the international community, and I will do my utmost to meet these expectations".
He said his priority would remain the assistance of the Lebanese authorities in their investigation of the February 2005 car bombing on the Beirut seafront that killed al-Hariri and 22 others.
He added that the investigating panel will provide the Lebanese with technical assistance, as appropriate, in their investigations into the attacks in Lebanon since 1 October 2004.
Syria protested on Thursday over comments by Brammertz's predecessor, German magistrate Detlev Mehlis, who was replaced last week at the end of his mandate.
Mehlis said in an interview in December that the Syrian authorities were responsible for the killing.
Damascus has sent an official letter of protest to the United Nations calling for Kofi Annan, the UN secretary-general, to take action.
"It is unacceptable that Mr Mehlis used the media during his last days in office as a means of pressure and to express a deep hatred against Syria," it said in the letter.
A number of Syrian officials have been interviewed in Vienna by UN investigators following an interim report which implicated Damascus in al-Hariri's killing. The commission wants to question Bashar al-Assad, the Syrian president.
The inquiry wants to question
the Syrian president
In the interview in question in December, Mehlis replied "yes" when asked by the Arab daily Asharq Al-Awsat if he was "perfectly convinced of Syria's responsibility in the murder of al-Hariri".
"The Syrian authorities are responsible," he said, but refused to go into details.
Brammertz, 43, was a deputy prosecutor of the International Criminal Court, in charge of the investigations division. Previously serving as Belgium's federal prosecutor, he has written extensively on global terrorism, organised crime and corruption.