GENEVA, Jan 19 (Reuters) - U.N. Syria envoy Staffan de Mistura has been invited to peace talks in Astana convened by Russia, Turkey and Iran, his spokeswoman Yara Sharif said on Thursday, but his humanitarian advisor Jan Egeland said the U.N.'s role at the talks was still under discussion.

"I do however take it for granted that Russia, Turkey, Iran, will understand the immense responsibility they take upon themselves as guarantors of an agreement of another process to enable a new beginning for the civilian population of Syria," Egeland told reporters in Geneva.

(Reporting by Tom Miles and Stephanie Nebehay) ((tom.miles@thomsonreuters.com; +41 58 306 2006; Reuters Messaging: tom.miles.reuters.com@reuters.net))