"After my conversation with Theresa May, our positions remain far away. My Government will always defend the interests of Spain. If there are no changes, we will veto Brexit," Sanchez wrote on Twitter.
Gibraltar, which is claimed by Spain, is a British Overseas Territory. At the 2016 referendum, it overwhelmingly voted to stay in the European Union, however, it will have to leave the bloc together with the United Kingdom in March 2019.
READ MORE: UK Prime Minister May Announces Text of Brexit Declaration Agreed With EU
Despite Madrid's opposition to the Brexit deal, the draft political declaration on the future relations of the United Kingdom and the European Union after Brexit was agreed at the level of negotiators and in general at the political level on Thursday.