RIYADH, Saudi Arabia (AP) — Syrian opposition groups and rebel factions began talks in the Saudi capital of Riyadh on Wednesday in an effort to form a unified front ahead of proposed peace negotiations with Syrian President Bashar Assad's government.

The meeting is taking place under the auspices of Saudi Arabia, a key backer of Sunni opposition blocs pushing for Assad's ouster.

Saudi Foreign Minister Adel al-Jubeir wished the group success at the start of their talks before leaving the closed-door session, according to a statement released to the media.

The nearly five-year civil war in Syria has killed more than a quarter of a million people and triggered a refugee crisis of massive proportions.

The stakes are high for the two-day Riyadh meeting, during which the disparate and often competing opposition factions will be held to a tight deadline to agree on the outlines of a political solution to the crisis, as well as on who should represent them in the proposed talks with Assad's government.

A peace plan agreed to last month by 20 nations meeting in Vienna set a Jan. 1 deadline for the start of negotiations between Assad's government and opposition groups.

However, signs of divisions among the participants emerged quickly, when Ahrar al-Sham, one of the most powerful rebel factions in Syria, released a statement suggested a compromise vision for the country's future remains far from reach.

The ultraconservative group objected to the presence of some of the other participants at the meeting, claiming they are "closer to the (Syrian) regime than they are to the revolution," and the lack of proportional representation of some of the other Islamist groups fighting on the ground in Syria. It did not elaborate.

The group also vowed to "preserve the Islamic identity of our people, as well as the principles of our orthodox religion" and said it will oppose any conference outcomes that contradict its principles.

The Associated Press received a copy of the names of the delegates in attendance from a Saudi official close to the talks. The official, who spoke to the AP on condition of anonymity because he was not authorized to release the information, said some of the delegates met with Western and Russian diplomats in Riyadh ahead of the talks.

The United States and its allies are calling on the opposition to work toward a consensus ahead of the negotiations intended to lead to a transitional period in Syria and Assad's eventual removal.

U.S. State Department spokesman John Kirby stressed on Tuesday that the meetings in Riyadh will affect future negotiations.

"We're grateful for this meeting that the Saudis have convened and led. We're going to be watching the outcomes, obviously, very, very closely," he said.

The largest bloc at the meeting, with around 20 delegates, is the Western-backed opposition group known as the Syrian National Coalition. Also in attendance are representatives of the Syria-based National Coordination Body. In total, fewer than 10 women are taking part.

Rebel factions at the talks include the Western-backed Free Syrian Army, the Saudi-backed Jaysh al-Islam and Ahrar al-Sham — groups that had long rejected any negotiations with Assad's government so long as he remained in power.

Notably absent were Kurdish opposition factions, such as the People's Protection Units, which is known by its Kurdish acronym the YPG. It's the main Kurdish fighting force battling the Islamic State group in Syria. However, there are ethnic Kurds at the talks from among the broader opposition groups invited.

The YPG is participating in a concurrent conference in Syria's northern province of Hassakeh that is unrelated to the Riyadh gathering and that is led by the U.S.-backed Syrian Democratic Forces, of which the YPG is a member.

Over the past year, ties between Saudi Arabia and Turkey have strengthened around their mutual support for Sunni groups fighting Assad's Iranian-backed government. The decision to exclude Kurdish groups is widely seen as a gesture to appease Turkey, which is wary of Kurdish ambitions for an independent state in the region.

___

Associated Press writers Bradley Klapper in Washington and Zeina Karam in Beirut contributed to this report.