"Prime minister Mikati hopes to finalize his consultations and form the government this week," the official, who is close to the premier, told AFP on condition of anonymity.
"The next government will include representatives of the (Hezbollah-led) new majority, centrists and technocrats," he said, adding that the size of the cabinet had not been finalised yet but would likely count 24 to 30 ministers.
The "centrists" would be appointed into office by Mikati and President Michel Sleiman, who is widely perceived as a politically neutral figure in Lebanon.
Hezbollah, which is backed by both Tehran and Damascus, last month toppled the Hariri government and succeeded in ushering Mikati in to replace him, thanks to the key parliamentary votes of its Christian and Druze allies.
The move prompted a wave of anger among the allies and supporters of US- and Saudi-backed Hariri, who accuse Shiite Hezbollah of a "coup" and of attempting to unilaterally control government.
Amin Gemayel, a Christian ally of Hariri, announced late Monday that talks on their alliance's participation in government had reached a dead end.
At the centre of the political deadlock is the UN-backed Special Tribunal for Lebanon, which is investigating the February 2005 assassination of Sunni ex-premier Rafiq Hariri, Saad's father.
Hezbollah had been pressuring Saad Hariri for months to disavow the tribunal before it forced the collapse of his government on January 12 over the tribunal.
The court is reportedly poised to indict Hezbollah members in connection with the Hariri case, a move the militant movement has warned against.
While Hezbollah has demanded Lebanon end all cooperation with the tribunal, the outgoing Hariri has sought a commitment from fellow billionaire Mikati to see the investigation through.
But Mikati has refused to make any promises on the issue.
"The prime minister designate's response to the demands of Hariri's camp have not changed from the beginning and he cannot make any commitments to either side as that would cause him to lose his position as a centrist," said the official working with Mikati.
The United States, France and other countries have adopted a wait-and-see approach to Mikati's appointment while he forms his government and tackles the thorny issue of the tribunal.