The White House said Friday it does not see any role for Syrian president Bashar al-Assad in a prospective political transition in Syria.
Earnest said the administration's immediate priority was removing Assad from power so he would "no longer have his hands on the weapon of war that are being used to slaughter thousands of people."
Earlier this week, the Russian government reported that representatives of the Assad regime had agreed in principle to participate in an upcoming peace conference. But Russian Foreign Ministry spokesman Alexander Lukashevich said the regime voiced opposition to Assad's resignation as a precondition of an eventual peace deal.
Earnest said Friday that the formulation of a transitional government was a "work in progress," acknowledging difficulties organizing rebel forces.
"This is hard work. This is not going to be an easy step. All these steps are hard. But this administration is committed to doing it," Earnest said.
He also stressed that the United States had asked Russia to stress to regime negotiators "that Assad must go."
"In the context of these discussions, we've asked the Russians to show responsibility, to exercise their influence over the Assad regime to make sure that the negotiators that appear are empowered to negotiate," Earnest said.
The White House was also asked about reports that Nicole Mansfield, and American woman from Michigan who had traveled to Syria to fight alongside rebel forces, had been killed. Earnest avoided commenting directly on the report, but said Americans should heed warnings about international travel.
"If there are Americans that are contemplating a trip to Damascus, I'd encourage them to consult with the State Department," Earnest said.