(CNN) The United Nations Security Council on Friday approved a resolution that supports international efforts to seek a political solution in Syria.

U.S. Secretary of State John Kerry said the process is designed to end the nation's civil war and provide a new government in Syria.

Russia and the United States both approved the resolution, even though it doesn't address the major issue separating those two nations: What will happen to Syrian President Bashar al-Assad? Russia supports Assad but the United States wants him removed.

Still, the accord was hailed as a major step toward bringing peace to Syria, where a civil war has killed thousands and sent millions of refugees fleeing into other nations.

"It's going to be uphill," said U.N. Envoy to Syria Staffan de Mistura. "It will be complicated. But it will be possible."

"This council is sending a clear message to all concerned," Kerry said. "The time is now to stop the killing in Syria and to lay the groundwork for a government the people of that battered land can support."

Besides recognizing the 17-nation International Syrian Support Group's efforts in the peace process, the resolution provides a rough timeline for political change in Syria.

It calls for "credible, inclusive and nonsectarian governance" within six months and "free and fair elections, pursuant to the new constitution," within 18 months.

The resolution, which passed 15-0, seeks a ceasefire in Syria. Kerry said that ceasefire would not include ISIS.

Kerry said some Security Council nations disagree on Assad's future but that nations involved in writing the resolution didn't want that issue to stop the peace process. Ending the war and bringing political stability to Syria go hand in hand, he said.

"If the war is to end, it is imperative that the Syrian people agree on an alternative in terms of their governance," he said.

Russian Foreign Minister Sergey Lavrov warned against the "demonization" of Assad, which he said happened to leaders like Moammar Gadhafi in Libya, who ended up being killed. That would not help the peace process, he said.

The resolution has a schedule for changing the political situation in Syria.

"We hope this process will not be protracted ad infinitum," Lavrov said.

Senior State Department officials told CNN that Kerry and Lavrov led negotiations Friday to fine-tune the text of the U.N. resolution.

Friday's meeting of the International Syria Support Group, or ISSG, the third in six weeks, sought to put in place a peace plan reached by ministers last month in Vienna under the umbrella of the United Nations.

The resolution does three things, which internationalize efforts to seek a political solution in Syria. It endorses the 17-member ISSG as the main body dealing with the Syria peace process; validates the peace plan agreed to by the ISSG in Vienna last month, including a ceasefire between the regime and opposition in six months and talks leading to drafting a new constitution; and gives the United Nations a leading role in working with the regime and opposition on negotiating a ceasefire and drafting a constitution, which officials said is aimed at putting an international stamp on the peace process.

Diplomats close to the talks said Friday that there is heated discussion among the nations in the meeting about the list of groups that will be considered terrorist groups and unable to take part in talks.

But they said it was unlikely to affect passage of a U.N. resolution giving international endorsement of the peace process.

"The consensus is that they won't reach consensus on the terrorist list today," one of the diplomats said.

Spurred on by the deadly attacks in Paris, the 17 nations overcame their differences on how to end the civil war in Syria and agreed to the road map for a political transition now being worked on.

The United States and Russia have long split on the best path forward in Syria. The United States supports groups warring with Assad, a close Kremlin ally. Moscow, meanwhile, has been bolstering Assad with airstrikes ostensibly aimed at ISIS but more often, according to the Pentagon, targeting other opposition fighters, including ones supported by Washington.

Not only have Russian military strikes had a minimal effect on ISIS, being mostly focused elsewhere, they have also exacerbated an already dire humanitarian crisis.

But an increasingly bloodied Russia -- now a target of ISIS -- and growing U.S. urgency in resolving the 5-year-old conflict whose chaos only strengthens the terror group, seems to provide some common ground for finding a resolution to the conflict.

After holding marathon meetings in Moscow with Russian President Vladimir Putin and Lavrov, Kerry said the United States and Russia hoped to enshrine the agreed-upon road map for an end to the civil war in a U.N. Security Council resolution.

The United States hopes a ceaseire between the regime and Syrian rebels would allow Russia, along with the U.S.-led coalition of Arab and Western allies, to focus on fighting the jihadists.

"You can't defeat Daesh without also de-escalating the fight in Syria," Kerry said in Moscow, using another name for ISIS.

State Department Spokesman John Kirby said Friday's meeting seeks to "better define" what a political transition in Syria would look like and how a ceasefire could be implemented and monitored.

Still undecided is which rebel groups should be part of the negotiations between the regime and the opposition, expected to start in early January.

Friday's talks follow a meeting last week in Saudi Arabia in which Syrian opposition groups agreed to unite to negotiate with the regime on a ceasefire. The Kremlin has rejected the results of the meeting in Riyadh, saying it considered some of the rebels present terrorists.

The question of whether Assad could take part in the political transition continues to be a main sticking point. For the past four years, the United States has sided with Gulf States in calling for Assad's ouster.

Photos: Tense moments between Obama and Putin Barack Obama and Russian President Valdimir Putin toast during a luncheon hosted by United Nations Secretary-General Ban Ki-moon during the 70th annual U.N. General Assembly on September 28 in New York City. Hide Caption 1 of 7 Photos: Tense moments between Obama and Putin Obama and Putin shake hands while posing for a photo ahead of their meeting at U.N. headquarters on September 28 in New York. Hide Caption 2 of 7 Photos: Tense moments between Obama and Putin Putin speaks with Obama during the Asia-Pacific Economic Cooperation summit in Beijing, China on November 11, 2014. U.S.-Russia relations have descended to a new low since Russia annexed Crimea in March. Hide Caption 3 of 7 Photos: Tense moments between Obama and Putin Obama and Putin share a comical and awkward moment on a large split-screen during an international ceremony on the stretch code-named Sword Beach, in Ouistreham, France, to commemorate the Allied invasion of Normandy on June 6, 2014. Obama and Putin had an informal 15-minute chat during lunch at the ceremony that marked the 70th anniversary of the D-day landings. "It's a positive thing that they spoke, but more needs to be done," a senior U.S. official said at the time. Hide Caption 4 of 7 Photos: Tense moments between Obama and Putin Putin greets Obama at the G-20 summit on September 5, 2013 in St. Petersburg, Russia. The United States and Russia have been squaring off over the bloody civil war in Syria. Hide Caption 5 of 7 Photos: Tense moments between Obama and Putin Obama listens to Putin after their bilateral meeting in Los Cabos, Mexico on June 18, 2012 on the sidelines of the G-20 summit. The meeting was the first time Obama and Putin held face-to-face talks since Putin returned to the president's office earlier that year. Obama said he and Putin discussed the conflict in Syria and "agreed that we need to see a cessation of the violence, that a political process has to be created to prevent civil war." Hide Caption 6 of 7 Photos: Tense moments between Obama and Putin Obama, who had become U.S. President six months earlier, enjoys tea with then-Prime Minister Vladimir Putin and members of the American delegation at Putin's dacha on July 7, 2009 in Moscow. Hide Caption 7 of 7

But this week in Moscow, Kerry raised eyebrows when he said "the United States and our partners are not seeking so-called 'regime change,' as it is known in Syria."

Some viewed Kerry's statement as an effort to placate his Russian hosts. Kerry did add that the United States still did not believe Assad "has the ability to be able to lead the future Syria," and soon after his remarks, the State Department said the U.S. policy that Assad should go remained unchanged.

Russia is now agreeing to the drafting of a new constitution and new elections, a position that has evolved over the last few months.

But Fred Hof, a former top U.S. diplomat handling Syria now at the Atlantic Council, warned that regardless of Assad's fate, until Russia and Iran are willing to press him to stop bombing the Syrian people, there is little hope the political process will yield any results and that the bloodshed will end.

"Stopping the mass murder is a good place to start," he said. "How the hell do you sit down for a peace process featuring compromise when one of the parties doesn't accept the rules of the game and the other party's constituency is being blown away on a daily basis?"

He continued, "The first symptom of Assad being under control would be an end to the collective punishment and mass homicide and only then would the Syrian people truly have a chance to decide their fate."