GENEVA (Reuters) - Peace talks being prepared later this month in the Kazakh capital of Astana should aim to consolidate Syria's ceasefire and pave the way for wider U.N.-backed negotiations in February, the U.N. Special Envoy Staffan de Mistura said on Thursday.

Turkey and Russia brokered the Dec. 30 cessation of hostilities and have pledged to work to open up access for aid agencies to deliver supplies across Syria, his humanitarian adviser Jan Egeland said.

But Egeland voiced disappointment that despite the ceasefire "largely holding", U.N. aid convoys have been denied access to five of 21 locations this month, including places in Rural Damascus, Homs and Hama.

(Reporting by Stephanie Nebehay and Tom Miles)