Assad's proposal, delivered in a speech Sunday in which he ruled out talks with rebels and rejected international peace proposals, "is yet another attempt by the regime to cling to power and does nothing to advance the Syrian people's goal of a political transition," State Department spokeswoman Victoria Nuland said.
"His initiative is detached from reality, undermines the efforts of Joint Special Representative Lakhdar Brahimi, and would only allow the regime to further perpetuate its bloody oppression of the Syrian people," she said.
Brahimi, the U.N.-Arab League envoy to Syria, had no immediate comment on Washington's assessment or on Assad's brushoff, which came 13 days after Brahimi met with Assad in Damascus, the Syrian capital, in a push for a negotiated solution.
"We don't want anyone to come to Syria to tell us what should be done for a political operation," Assad said in Damascus Opera House. "Everyone who comes to Syria knows [that] Syria accepts advice, but doesn't take dictation."
People briefed on Assad's meeting with Brahimi told The Wall Street Journal Assad insisted only he could steer Syria out of the crisis. They said he told the veteran Algerian diplomat he would lead Syria until his term ends next year and then run again, the Journal said.
"Who should we negotiate with? Terrorists?" Assad told the opera house audience.
"The enemies of the people are the enemies of God, and the enemies of God will burn in hell."
The opposition Syrian National Coalition, which has gained political recognition from more than 100 countries, including the United States, said Assad's address marked the end of international efforts to negotiate a settlement.
It called the speech "a pre-emptive strike against both Arab and international diplomatic solutions equally."
The foreign ministers of Turkey, Britain and the European Union dismissed Assad's nearly hourlong address and reiterated calls for him to resign.
Assad's speech was filled with "empty promises," Turkish Foreign Minister Ahmet Davutoglu said told reporters in the Aegean port city of Izmir.
"It seems he's locked himself up in a room and only reads the intelligence reports presented to him," Davutoglu said.
British Foreign Secretary William Hague said on Twitter Assad's speech was "beyond hypocritical."
"Deaths, violence and oppression engulfing Syria are his own making," his Twitter message said, adding, "empty promises of reform fool no one."
EU foreign policy chief Catherine Ashton's office said in a statement the 27-nation bloc would "look carefully if there is anything new in the speech, but we maintain our position that Assad has to step aside and allow for a political transition."
Egyptian President Mohamed Morsi told CNN he supported calls for Assad to be tried for war crimes.
The plan Assad proposes calls for a multiphase political process, beginning with foreign governments halting their funding and supplying of weapons to rebels. That would be followed by a national dialogue that would exclude much of the current opposition leading the battle against his regime.
After that would come a new Constitution approved by referendum and then a coalition government, he said.
Assad's last public speech was in June. He told Russian TV in November he would "live and die in Syria."
The opposition Local Coordination Committees of Syria said at least 101 people died in Syria Sunday, including two children and 10 women. Twenty-eight were killed in Damascus and its suburbs, the group said.