The United States is talking to Russia and other powers about a new round of international discussions on the crisis in Syria, the State Department says.
But no date or guest list has been confirmed for the talks, and the US State Department admitted on Monday (local time) that the situation was complex and that talks may drag on.
"We need a plan for a political transition that can work," spokesman John Kirby said.
"But it's not as if we're approaching this without a sense of urgency."
US Secretary of State John Kerry spoke by telephone with his Russian counterpart Sergei Lavrov about plans for a broader dialogue to bring an end to the civil war.
"They talked about the next round of discussions and what each of them had in terms of expectations for that meeting and future meetings," Kirby said.
Kerry, Lavrov and their counterparts from Saudi Arabia and Turkey met last week in Vienna on the conflict, after which they said more talks were planned.
But neither Moscow nor Washington have publicly given a date or a location for the next round of discussions, which could come as early as Friday.
"This is about coming together to try to reach a consensus view on what an effective political transition can look like in Syria," Kirby said.
"And that's complicated," he added, warning that finding an enduring solution will take time.
Responding to reports that the group could meet on Friday in Vienna, Russian foreign ministry spokeswoman Maria Zakharova said: "We're working on it.
"I cannot share any concrete details with you so far apart from the fact that we are actively working with other capitals on Syria to build on the Vienna meeting."
France is to convene separate talks in Paris on Tuesday, but the State Department could not immediately confirm if any US envoy will attend.
Syria is in the grip of an overlapping series of conflicts between Bashar al-Assad's regime, opposition rebels, Kurdish groups and jihadist extremists.
Adding to the chaos, a US-led coalition and a Russian task force are conducting parallel but uncoordinated air strikes against Islamist rebels.
Washington sees the root cause of the conflict as Assad's brutality towards his own people and refusal to step aside to allow a political peace process.
But Moscow insists he remains a legitimate leader and that the priority must be the defeat of the Islamic State group and Al-Qaida linked jihadists.
Despite their deep disagreements over the cause of the strife, Kerry and Lavrov have taken the lead in trying to find a consensus on how talks could begin.
But progress has been slow and, as fighting continues, tens of thousands of desperate refugees continue to make their way from the region to Europe.