The head of the UN refugee agency on Tuesday said he was "deeply concerned" by a proposed deal between the EU and Ankara to curb the migrant crisis that would involve people being sent back to Turkey.

"As a first reaction I'm deeply concerned about any arrangement that would involve the blanket return of anyone from one country to another without spelling out the refugee protection safeguards under international law," UNHCR chief Filippo Grandi told the European Parliament.