Free Syrian Army fighter fires a shell towards ISIS fighters in the northern Aleppo countryside, Syria, January 18, 2016.

The United Nations on Monday said it was waiting for regional powers spearheading the Syria peace process to agree on who will take part in talks starting in just one week’s time and raised the possibility of a delay.

The peace talks, the first between the Syrian government and the opposition since 2012, are scheduled to open in Geneva on January 25, but invitations have yet to be sent to the delegations.

The 17 countries pushing for a peace deal, including the United States, Russia, Saudi Arabia and Iran, have been struggling to agree on the list of opposition leaders who will have a seat at the negotiating table.

“At this stage, the UN will proceed with issuing invitations when the countries spearheading the international Syrian Support Group process come to an understanding on who among the opposition should be invited,” said UN spokesman Farhan Haq.

U.N. Secretary-General Ban Ki-moon “urges those countries to redouble efforts to reach that agreement,” he said.

The Geneva talks are to pave the way to a new constitution and elections in 18 months to end Syria’s nearly five-year war, which has killed more than 260,000 people and triggered a mass refugee exodus to Europe.

The U.N. spokesman said there were “concerns about arrangements” that had yet to be resolved for the talks to go ahead and added: “If there is any kind of slippage, we will let you know.”

A council diplomat separately said “it’s going to be difficult” to reach agreement on the list of participants.

The U.N.’s Syria envoy, Staffan de Mistura, told the U.N. Security Council during a closed-door briefing that “additional work needs to be done” before he can send out invitations, Churkin told reporters.

But he added that January 25 remained the target and that it was “important to stick to that date.”

Asked about the prospects for a delay, Uruguay’s Ambassador Elbio Rosselli, who holds this month’s council presidency said that “no different date was considered today.”

During his briefing to council members, De Mistura stressed the importance of lifting sieges and allowing more humanitarian aid to reach civilians, many of whom have been surviving on very little food.

Russian President Vladimir Putin held talks in Moscow with the emir of Qatar on the Syrian crisis.

Russian Foreign Minister Sergei Lavrov said both Moscow and Doha were expecting that, in accordance with a U.N.-backed plan, talks between the Syrian government and the opposition would begin “in the nearest future, already this month.”

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