"Today the news is awful," Mogherini said in an interview with media organisations in Brussels on the sidelines of a EU-UN conference that was meant to focus on the post-conflict situation in Syria.
"But this is a dramatic reminder that the situation on the ground continues to be dramatic in many parts of Syria," Mogherini said.
"Obviously there is a primary responsibility there of the regime because it has responsibility of protecting its people not attacking its people."
It is also looking at "post-agreement assistance" once troubled UN-backed peace talks move forward, the EU said.
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Former Italian foreign minister Mogherini admitted it was surreal" to be talking about the post-conflict situation but said the world had to plan ahead.
"I know it can sound surreal to start planning peace when in middle of conflict but... You hear this more than anything else, they want peace and want to get out of this terrible situation," she said.
"The message is on the human side we do not want to see the human support for Syria and Syrians diminishing," she said.