EU shuns Russian-backed Syrian refugee talks
More than half of Syria's population have fled their homes since civil war erupted in 2011, and some 5.5 million are sheltering abroad, mainly in Turkey, Lebanon and Jordan.
But Assad's forces now hold 70 percent of the country, thanks to military support from Moscow and Tehran, and he wants to hold a two-day conference in Damascus from Wednesday on bringing Syrians home.
Russia's President Vladimir Putin has backed the idea.
But EU foreign policy chief Josep Borrell said EU members would not take part as the situation is not yet safe for returns.
"The EU and its member states will not attend this conference," Borrell said, adding that he and the foreign ministers of "a number" of EU countries had been invited.
"While the decision to return must always be an individual one, conditions inside Syria at present do not lend themselves to the promotion of large-scale voluntary return, in conditions of safety and dignity in line with international law."
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Borrell argued that Syria's priority must be "to create conditions for safe, voluntary, dignified and sustainable return of refugees" in line with guidance from the UN High Commissioner for Refugees.
And he reiterated that "the regime and its sponsors" should engage with the peace process mandated under a UN Security Council resolution and release its detainees.