Foreign Minister Walid al-Moualem's comments showed the government has dug in against foreign pressure for a deal with the rebels fighting to topple Assad.
"No one should dare discuss the position of the president ... this is unacceptable," he told Syrian state television in an interview.
World powers have been deadlocked in their efforts to promote a transitional government they hope could prevent more bloodshed in the 22-month-old uprising against Assad, which has turned into a civil war that has killed more than 60,000 people.
United Nations and Arab League envoy Lakhdar Brahimi, who recently visited Assad and Syrian officials, told Reuters a week ago Assad should not be part of a transitional government.
Syrian officials condemned his comments and said the mediator was biased toward governments supporting the rebels.
Moualem said Assad's proposal earlier this month for a new parliament and constitution was the only way forward out of the conflict. He reiterated the embattled leader's argument that only "nationalistic opposition" could participate.
Their definition excludes the armed opposition or any group that supports intervention in Syria's conflict, even though they are now the driving force of the rebel movement.
The opposition, for its part, has rejected anything but Assad's removal.
International talks in Geneva last June, led by Brahimi, proposed a transitional government but left open Assad's future. The proposal foundered after opposition backers like the United States insisted Assad not play a role, while Russia, Assad's main arms supplier, said foreign powers should not impose restrictions on the transition.Syrian interpretation of Geneva plan
In his interview with Syria TV on Saturday, Moualem said Assad's proposed initiative for national dialogue was Damascus's only accepted reading of the Geneva transition plan.
"There were a lot of ambiguities (in the Geneva proposal) and we were unable to clarify them. So this Syrian political program is our interpretation of the transitional period mentioned in the Geneva declaration," he said.
"We will not discuss anything outside of this program."
Assad's pitched a three-stage initiative earlier in January which calls for national dialogue, creation of a new constitution, and a new parliament, followed by national referendums. But the reforms are similar to previous ones made by the Assad, which the opposition rejected as superficial.
Moualem said all those who wanted reform would accept it.
"What more democracy could one want than this?"
The current government, he said, would lay the groundwork for dialogue and transition over the next two to three months. He said efforts would continue despite daily clashes, which now regularly kills more than 100 Syrians per day.
"The question is if the violence doesn't stop should we continue with the dialogue or not? I say we should continue."
The minister also said that Syria's borders, a large portion of which have fallen into rebel hands, should be brought back under control by international efforts.
"This issue is actually something for the United Nations. They should come up with a mechanism, but what mechanism? It must be something that the Syrian government agrees to."
BEIRUT (Reuters) -- Syria's foreign minister said on Saturday any discussion of President Bashar Assad's future was "unacceptable", a week after an international envoy said the president should not be part of a transitional government.