MADRID—Spanish Prime Minister Pedro Sanchez described Morocco’s actions during a crisis two weeks ago when thousands of illegal immigrants crossed into Spain’s north African enclave of Ceuta as unacceptable and an assault on national borders. Asked at a news conference on Monday about comments by the Moroccan foreign minister, who linked the immigrant crisis to the disputed territory of Western Sahara, Sanchez said, “It is not acceptable for a government to say that we will attack the borders, that we will open up the borders to let in 10,000 migrants in less than 48 hours … because of foreign policy disagreements.” Two weeks ago, thousands of people swam around the border or scaled the fence separating Ceuta from Morocco over two days after Moroccan security forces appeared to loosen border controls. Most were immediately returned to Morocco but hundreds of unaccompanied minors, who cannot be deported under Spanish law, remain. …