Spain’s opposition parties are taking aim at Prime Minister Pedro Sánchez’s migration policies following the arrival of tens of thousands of unauthorized migrants in the Spanish exclave of Ceuta.

Over the past 24 hours, the migrants have forced their way into the heavily fortified autonomous city, which covers 18.5 square kilometers on the northern coast of Africa. With the Civil Guard forces that normally defend Ceuta overwhelmed, the Spanish army was mobilized late on Thursday to secure the border.

Speaking from Ceuta, where he flew to meet with officials overseeing the crisis on Friday, Sánchez characterized the situation as “an attack, a violation of the territorial integrity of Spain.”