Russian Foreign Minister Sergei Lavrov, left, meets with Secretary of State John Kerry in Vienna. (Russian Foreign Ministry Press Service/EPA)

New international negotiations on Syria that will start Friday follow weeks of intensive diplomacy, a significant amount of arm-twisting on all sides, and agreement between the United States and Russia that the future of Syrian President Bashar al-Assad will not be on the table for now.

In the lead-up to the talks, Secretary of State John F. Kerry and his Russian counterpart have stipulated in near-daily conversations that their ongoing disagreement about where a Syrian political transition must end — with the United States insisting Assad must go, and Russia demanding the opposite — should not prevent the process from starting.

At least a dozen countries, including Assad-backer Iran as well as U.S. allies in Europe and the region, will attend the talks in Vienna. “This is the most promising opportunity for a political opening we’ve seen in years,” Kerry said in a speech Wednesday.

His optimism was in stark contrast to the backdrop of growing civil war carnage that will benefit only the Islamic State; a rising flood of Syrian refugees in Europe; and what some have described as a new Cold War after Russia’s entrance into the Syrian conflict.

The alliance between Russia and the regime of Bashar al-Assad goes back decades. Here's a bit of historical context that explains why Russia is fighting to prop up its closest ally in the Middle East. (Ishaan Tharoor and Jason Aldag/The Washington Post)

The Russian bombing campaign, focused on Assad’s opponents, is neither “smart nor moral,” Kerry said. But now that Moscow has intervened, he indicated, it was time for all sides to concentrate on their shared concerns.

“We agree that the status quo is untenable and we must find a way to end the conflict,” Kerry said of Washington and Moscow. “We agree that a victory by [the Islamic State] or any other terrorist group has to be prevented. We agree that it is imperative to save . . . state institutions and preserve a united, secular Syria.

“We agree that we must create the conditions for the return of displaced persons and refugees. We agree on the right of the Syrian people to choose their leadership through transparent, free and fair elections with a new constitution and protections for all minorities.”

Few of the participants in the upcoming talks, which follow more than three years of inconclusive international meetings and global hand-wringing while the situation in Syria has continued to deteriorate, believe there is much chance of success.

“We want to be team players,” said a senior official of one U.S. ally in the Middle East. “I’m skeptical this will actually lead anywhere.” Noting Kerry’s description of areas of U.S.-Russia convergence, the official said that “we all agreed on that before” in previous discussions. It’s “when we get to specifics,” such as what happens to Assad, the official said, that “it all falls apart.”

A top European diplomat noted that his government is still in the dark about how the meeting and an anticipated series of follow-on sessions, driven largely by Kerry, will be structured. Foreign officials and Obama administration officials agreed to discuss the diplomacy and agreements leading up to the talks on the condition of anonymity.

U.S. officials said that many of the details are to be determined and that at this point Kerry is primarily focused on having all those with competing interests sit in the same room and acknowledge how bad the situation has gotten.

Beginning with an initial meeting last week among the United States, Russia, Turkey and Saudi Arabia, administration officials previewed what Kerry hopes will be a rapidly evolving series of intensive discussions over the coming weeks, perhaps further widening the circle of participants. A key early objective is to create facts on the ground, including potential cease-fires, that will change the current momentum.

At some point, officials said, skeptical Syrians on both the government and opposition sides will have to be brought into the talks. U.S. officials are optimistic that if agreements can be reached among those who are supplying both Assad and his opponents, and bombing on their behalf, they will have little choice but to come on board.

It is, administration officials acknowledged, a long shot.

Much of the recent effort has centered on deciding who should come and then convincing them to participate. After last week’s meeting, Russia said it had little interest in continuing unless Iran was invited.

Iran’s supreme leader had said Tehran would not negotiate any issue with the West beyond the just-concluded nuclear deal. One senior European diplomat who visited there this month came away convinced that neither Iran’s hard-liners nor those who advocate more diplomacy with the West had any interest in distractions from their laser focus on the end of economic sanctions that will come with implementation of the nuclear accord early next year.

At the same time, this diplomat and others said, Iran fears being sold out at the table by Russia, its ally-of-convenience in Syria, and the Russians themselves argued that it was better to be a key player inside the tent than an outside observer.

The attendance of Iranian Foreign Minister Mohammad Javad Zarif, announced in Tehran on Wednesday after a series of telephone conversations this week with Moscow, will mark the first major diplomatic contact between Iran and the United States since they reached the nuclear agreement in July.

Saudi Arabia, which had vowed that it would never participate in Syria talks that included Iran, had a series of similar conversations with the United States before agreeing to attend. But the Saudis, and others who share their determination to end Assad’s rule, have also been given some sweeteners.

Kerry described the talks as half of a “two-pronged” strategy that also includes stepped-up assistance to anti-Assad forces and a willingness to allow Saudi Arabia and others supplying them with U.S.-made weapons to increase both the quantity and quality of that aid, officials said.

At the same time, the administration has increased assistance to Syrian Arab and Kurdish forces­ fighting against the Islamic State and said it is planning a significant escalation in airstrikes against the militants. President Obama is considering proposals to allow U.S. Special Operations forces­ to begin limited ground operations in support of the Syria strikes.

But the key to both starting the talks and ending them successfully lies with the United States and Russia, officials from a number of negotiating countries said.

“When Russia got involved” in Syria, said a diplomat from the region, “the first reaction was that this was no longer a regional issue. It is not something that Saudi Arabia or Turkey or others can fix.”

“Now, if Russia and the United States can’t resolve it,” the diplomat said, “what the hell are we going to do?”

Carol Morello and Brian Murphy in Washington, and Erin Cunningham in Cairo contributed to this report.