President Assad of Syria meets Putin in Moscow.

Bashar Assad's surprise meeting with Vladimir Putin could signal that Russia ultimately seeks a political settlement after weeks of heavy airstrikes in Syria. But the terms of such an arrangement are uncertain, and questions remain about whether Moscow will seek the departure of its longtime ally or try for a power-sharing agreement. In a further sign that a diplomatic push might be underway to end the four-year crisis, Russia announced Wednesday that Foreign Minister Sergey Lavrov and U.S. Secretary of State John Kerry had agreed to meet Friday in Vienna with their counterparts from Saudi Arabia and Turkey — both firm Assad critics.

The Syrian president's visit to Moscow, his first known trip abroad since war broke out in 2011, was announced on Wednesday, the morning after it happened, and raised intense speculation about the two leaders' motives — and a strong response from Washington. "We view the red-carpet welcome for Assad, who has used chemical weapons against his own people, at odds with the stated goal by the Russians for a political transition in Syria," said White House spokesman Eric Schultz.

If nothing else, it underscored how emboldened the embattled Syrian leader has become in the wake of the Russian airstrikes that began on Sept. 30 and Iran's deployment of hundreds of ground forces to fight alongside Syrian government troops. Russia says it is targeting militants, especially those of the extremist Islamic State group. But critics, including the U.S., say Moscow's military intervention props up Assad and is likely to fan the violence.

In a statement, Putin said that along with fighting militants, Moscow believes that "a long-term settlement can only be achieved as part of a political process with the participation of all political forces, ethnic and religious groups." In separate comments posted on the Syrian presidency's official Facebook page, Assad said the Russian military operation in Syria had helped to halt the spread of terrorism and that a political solution could only come after that threat was addressed.

"Terrorism which we see spreading today could have been more widespread and more harmful if it weren't for your decisions and steps," Assad told Putin in the remarks carried by Arab media. The threat of terrorism, he said, "obstructs" any political solution to the crisis. Yet how long Russia is willing to continue its expensive and politically volatile airstrikes is open to question.