Russian President Vladimir Putin, left, embraces Syrian President Bashar al-Assad Monday in the Bocharov Ruchei residence in the Black Sea resort of Sochi, Russia. (Mikhail Klimentyev/AP)

Russian President Vladimir Putin launched a major new push Tuesday to end the war in Syria after an unannounced visit by Syrian President Bashar al-Assad to Russia that seemed to affirm his future role in any eventual settlement.

The Russian initiative builds on an agreement reached with President Trump this month in which the United States effectively acknowledged Russia’s lead role in Syrian diplomacy in return for Russian acceptance of a continued U.S. role in Syria now that the Islamic State is nearing defeat.

After Putin’s meeting with Assad, the Russian president spent much of Tuesday on the phone with regional and world leaders, seeking their support for proposals that would parlay Russia’s successful military intervention on Assad’s behalf in 2015 into a diplomatic victory that would seal Russia’s role as an important world player.

The spurt of diplomacy began with an announcement by the Kremlin that Assad had met with Putin on Monday in the Russian resort town of Sochi, where photographs released by Russian media showed the two men warmly embracing.

Putin told Assad that the war in Syria is as good as over and urged him to turn his attention to securing a political solution to the conflict, according to comments broadcast by state media.

“As far as our joint work in fighting terrorism on the territory of Syria is concerned, this military operation is indeed nearing completion,” Putin said. “I believe that the main task now is to launch the political process.”

Putin then talked for more than an hour on the phone Tuesday with Trump, a conversation that focused mostly on Syria, according to readouts of the conversation from both the Kremlin and the White House. Putin told Trump he had secured a commitment from Assad to cooperate with the Russian initiative, including constitutional reforms and presidential and parliamentary elections, the Kremlin said.

The White House said the two leaders reiterated their commitment to securing a settlement within the parameters of the U.N.-backed peace process in Geneva, as well as to ensuring a Syria that is free of “malign intervention” — a reference to Iran’s extensive influence there. “We’re talking very strongly about bringing peace for Syria,” Trump later told reporters in Washington.

Putin later telephoned Egypt’s President Abdel Fatah al-Sissi and Israeli Prime Minister Benjamin Netanyahu to relay details of his conversations with Assad, and was expected to call Saudi Arabia’s King Salman, the Kremlin said.

Tuesday’s conversations came on the eve of a key summit on Syria between Putin, Iran’s President Hassan Rouhani and Turkey’s President Recep Tayyip Erdogan that is also to be held in Sochi, which is emerging as the epicenter of the Russian push for a Syrian solution. Iran and Turkey are the regional players with the biggest influence over the parties in Syria.

That summit will kick off events in the coming weeks that Russia hopes will lead to a grand bargain over Syria, endorsed by all the global and regional players with a stake in the outcome of the war as well as by Syrians.

Smoke covers buildings following an air strike Nov. 18 on the rebel-held besieged town of Arbin, in the Eastern Ghouta region on the outskirts of Damascus. (Amer Almohibany/AFP/Getty Images)

Saudi Arabia is due to host a gathering of opposition leaders in Riyadh, also on Wednesday, in an attempt to forge an almost entirely new opposition body to represent the anti-Assad movement in future negotiations. Nearly a ­dozen leaders of the existing, U.S.-backed opposition grouping have submitted their resignations ahead of the meeting to protest what they fear is an abandonment of their allies’ commitment to securing Assad’s departure.

On Nov. 28, the United Nations is scheduled to host an eighth round of peace talks in Geneva between the government and the revamped opposition, a process that is ostensibly aimed at some form of transition away from Assad’s rule.

But the Trump-Putin deal omitted all references to any form of “transition,” and the emphasis now is instead on a process of writing a new constitution that will lead to elections.

On Dec. 2, Russia is planning to host a gathering of about 1,300 Syrians representing the revamped opposition, the government and a range of other groups to discuss the terms of a new constitution. After the document has been written, according to drafts of the Russian proposals, there will be elections in which Assad will be allowed to compete.

The diplomacy was facilitated by the agreement reached between Putin and Trump. The United States wields influence mainly over the northeastern corner of Syria, where a small contingent of U.S. troops has been helping Kurdish-led fighters battle the Islamic State. At least some of those troops are expected to remain behind now that the war is nearly over to stabilize the area pending a solution to the wider Syrian war, Defense Secretary Jim Mattis said last week.

Many questions remain however, including whether Assad is willing to abandon his stated goal of reconquering the territory that fell out of his control during the past six years of war. Though the Russian proposals would leave him in office, perhaps indefinitely, they would also dilute his powers and give his opponents a role in government.

Putin’s spokesman Dmitry Peskov told reporters that Putin had sought to assure world powers that Russia is prepared to guarantee Syrian compliance with any agreements reached. Russia would “work with the Syrian leadership to prepare the groundwork for possible understandings,” Peskov said, to “make sure” that any such agreements will be “viable.”

But Assad appeared to hedge his commitment to the process in comments reported by Russian media about his meeting with Putin. “We are interested in promoting the political process,” ­Assad said. “We hope Russia will support us by ensuring the external players’ noninterference in the political process, so that they will only support the process waged by the Syrians themselves.”

“We do not want to look back. We will accept and talk with anyone who is really interested in a political settlement,” Assad added.

It is also unclear whether Iran, Assad’s closest ally, will be willing to comply with an international deal that almost certainly would include pressure on Tehran to dilute the extensive influence it has secured through its dispatch of militias and money over the past six years.

Securing opposition acceptance of a continued Assad role will also be tough, even though international support for his departure is waning, Turkey’s Foreign Minister Mevlut Cavusoglu told reporters in Istanbul last week.

“It is not only Russia and Iran — now the U.S., even Saudi Arabia and France are more flexible on Assad,” Cavusoglu said. “But here we shouldn’t be emotional. We have to be very realistic. We need to unite all the different groups, and it seems it is not very easy to unite everybody around Assad, after seven years of civil war and after this regime killed 1 million Syrians.”

The war is widely estimated by monitoring groups to have killed between 300,000 and 500,000 Syrians, but the challenge of bringing about any form of reconciliation is nonetheless immense.

Loveluck reported from Beirut, and Filipov reported from Moscow. Kareem Fahim in Istanbul and David Nakamura in Washington contributed to this report.