Syrians make their way through debris as they leave for a safer place following air strikes in the rebel-controlled side of the northern city of Aleppo on January 13, 2016.

A prominent Syrian opposition politician said on Thursday he thought it unrealistic that peace talks will begin on Jan. 25 in Geneva as planned unless sieges are lifted and humanitarian aid for civilians allowed in.

A U.N envoy had earlier said the talks were still on schedule.

“I personally do not think Jan. 25 is a realistic date for when it will be possible to remove all obstacles facing the negotiations,” George Sabra told Reuters by telephone.

Sabra is part of a council formed in December that is tasked with overseeing negotiations to bring an end to the five-year-old conflict raging in Syria.

Rebel groups issued a statement on Wednesday saying they would not take part in peace talks unless attacks on civilians stop and humanitarian aid is given where needed.

The U.N. Special Envoy for Syria Staffan de Mistura said on Wednesday that Syria peace talks were still planned to start in Geneva on Jan. 25.

Sabra said the biggest obstacle is implementation of articles 12 and 13 of a U.N resolution passed last year, which call on all sides in Syria’s civil war to allow humanitarian access to those in need and halt attacks on civilians.

“There are still towns under siege. There are still Russian attacks on villages, schools and hospitals,” Sabra said. “There is no sign of goodwill.”

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