'For 72 hours, we found that in the documents of withdrawal and future relationship, it is not clarified something that is fundamental for us: Gibraltar does not belong to the United Kingdom, but is represented by the United Kingdom, ' said Sanchez.
A strategic port on Spain's southern shore at the mouth of the Mediterranean, Gibraltar - known by locals as The Rock - has been governed by Britain since the 1713 Treaty of Utrecht.
Theresa May has shot down attempts to include Gibraltar in the Brexit talks as she insisted the British Government would "never" discuss a change in the sovereign status of the territory without permission from the local Government.
The Spanish foreign minister, Josep Borrell, said his government wanted a clear promise that no future trade or security deals would apply to Gibraltar without Spain's consent.
"As things stand today if there are no changes regarding Gibraltar, Spain will vote no on Brexit", said Mr Sánchez.
This is because the article "could be interpreted that the future of Gibraltar is included in the negotiations of the future relations between the United Kingdom and the European Union".
North Korea to Expel US Citizen Detained for Illegally Entering State
North Korea has chose to deport a U.S. citizen detained for illegally entering the country, its state media reported on Friday. South Korean claimed this was "nothing new", and President Donald Trump claimed to have already known about the bases.
"It does not come as a surprise that Madrid should seek to raise new Gibraltar issues at the last minute on our negotiations to leave the EU".
"We are seeking a deal that works for the whole United Kingdom family and that deal must work for Gibraltar too".
"It is not realistic to expect Gibraltar to become part of Spain", Gomez Arana said, noting that a 2002 referendum saw 99 percent of the population say that it did not agree that Britain and Spain should share sovereignty of the territory.
"We, as a country, cannot assume that what will happen to Gibraltar in the future only depends on Britain and the European Union".
"There is an article that we only found out about on Wednesday", Borrell said, following a meeting of EU's European affairs ministers.
Another crucial item is the fate of cross-border workers, an important matter for Spain as there are around 10,000 Spaniards who cross for work into Gibraltar every day.
Spain's demands on Gibraltar are the latest push by European Union states to obtain more on national interests ahead of Sunday's summit of European Union leaders, but diplomats said there was little concern these would scupper prospects for a deal.