"There is no room, no space for any kind of mediation or international initiative or action," the BBC quotes Tusk as saying.
He was speaking at a joint news conference with EU Commission President Jean-Claude Juncker.
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Mr Tusk's remarks came hours after Spain said it was beginning the process of imposing direct rule on the autonomous region.
Read alsoCatalonia’s Puigdemont suspends independence declaration"I am of course for many reasons in permanent contact with (Spain's) Prime Minister Mariano Rajoy," Mr Tusk said.
"There is no hiding that the situation in Spain is concerning, but our position... is clear."