UNITED NATIONS - In a rare display of unity, the United Nations Security Council adopted a resolution Friday that calls for talks between the Syrian government and opposition groups as well as a ceasefire in the Arab nation's 5-year-old civil war that has taken a heavy toll of life and triggered massive population displacements.

However, the resolution doesn't mention what role Syrian President Bashar al-Assad will play. The Syrian leader is supported by close ally Russia, but the United States has said it would like to see him removed from power.

The disagreement has been a contentious issue in discussions on resolving the conflict, and Syrian opposition groups have said they will not participate in a ceasefire unless Assad agrees to step down as president.

Friday's resolution says elections must be held in the next 18 months but makes no mention of whether Assad will be able to run.

US Secretary of State John Kerry, who presided over the 15-member council's ministerial level session, said the resolution sends a message that "the time is now to stop the killing in Syria and lay the groundwork for a government" that does not leave Syrians with a choice between Assad and the Islamic State.

Delegates from across the world had gathered in New York earlier Friday to discuss the conflict, which has left 250,000 dead and caused millions of Syrians to flee, intensifying the ongoing migrant crisis in Europe. Kerry said the resolution sends "a clear message to all concerned that the time is now to stop the killing in Syria."

Still, the resolution acknowledged the conflict won't really end because it bars “terrorist groups” operating in the country, including the Islamic State and al-Nusra Front, from participating in the ceasefire.

Kerry also hosted a separate gathering of envoys from 20 countries in the International Syria Support Group that also sought ways to intensify the fight against the Islamic State, which holds large swaths of the country and has greatly exacerbated the war.

The resolution also calls for the UN to present the council with options for monitoring a ceasefire within one month.

Talks between Syria's government and opposition should begin in early January, the resolution said, though Kerry said mid-to-late January was more likely. It also endorsed the continued battle to defeat Islamic State militants who have seized large swaths of both Syria and neighbouring Iraq.

It was one of the strongest appeals for peace by the council, divided for years on the issue of Syria's war, since Russia and China began vetoing a series of Western-drafted resolutions on the conflict in October 2011.

The resolution came after Moscow and Washington hammered out a deal on a text. The two powers have had very different views on what should happen in Syria, where Islamic State militants control considerable territory that Western governments suspect has been a launch pad for attacks on Western nations and Russia.

Kerry made clear that there were still differences on the future of Assad, a close ally of Russia and Iran who Western countries want ousted, as well as on the question of which Syrian opposition groups will have a seat at the table in talks with the government.

"We are under no illusions about the obstacles that exist," Kerry said. "There obviously remain sharp differences within the international community, especially about the future of President Assad."

Russian Foreign Minister Sergei Lavrov said of the resolution: "This is a clear response to attempts to impose a solution from the outside on Syrians on any issues, including those regarding its president."

French Foreign Minister Laurent Fabius said the talks between the Syrian government and opposition would only succeed if there were credible guarantees on the departure of Assad.

"How could this man unite a people that he has in part massacred?" Fabius said. "The idea that he could once again stand for elections is unacceptable to us."

Syrian Ambassador Bashar Ja'afari said Assad's government was prepared to take part in the talks in good faith."I reiterate the readiness of the Syrian government to participate effectively on any sincere effort where the Syrians will determine their choices through dialogue under Syrian leadership and not foreign intervention," he said, adding all countries should coordinate with his government.

Agreement on a resolution came after a meeting of the so-called International Syria Support Group at New York's Palace Hotel. Foreign ministers from 17 countries, including Lavrov, Kerry and other European and Middle Eastern ministers, as well as top diplomats from regional rivals Turkey, Saudi Arabia and Iran, were in New York for the meetings.

The council, which met at foreign minister level, asked Secretary-General Ban Ki-moon to convene government and opposition representatives in formal negotiations early next month on a political transition as a step to lasting peace, in line with the 2012 Geneva Communique and consistent with the 14 November 2015 International Syria Support Group (ISSG) on the issue.

AFP adds: A UN-backed roadmap to end the Syrian war was met with scepticism Saturday by members of the country's fractured opposition who insist President Assad must go to achieve peace.

The UNSC plan was described as unrealistic by the Istanbul-based National Coalition, the main Syrian opposition grouping.

The resolution "undermines the outcome of the meetings of revolutionary forces in Riyadh and waters down previous UN resolutions concerning a political solution in Syria," coalition head Khaled Khoja said on Twitter.

Fellow coalition member Samir Nashar said bombing by the regime and Russia must stop for there to be a sustainable ceasefire.

"Given the reality on the ground and the impasse on the fate of Bashar al-Assad, the agreement is absolutely not applicable," he said.