The Spanish government is considering filing a complaint with the European Union against Algeria after the latter decided to suspend a friendship treaty.
An official Spanish source said that the suspension could violate the agreement signed in 2005 between the southern Mediterranean countries and the European community.
Algeria was angered when Spain said in March that it supported a Moroccan plan to offer autonomy to Western Sahara.
Speaking to Asharq Al-Awsat, the source added that the Spanish Foreign Ministry was preparing an appropriate and constructive but firm response in defense of the interests of Spain and Spanish companies.
Spain was surprised after Algeria's banking association on Wednesday ordered stopping payments to and from Spain, affecting all trade except gas supplies.
The Spanish government is considering the repercussions at the local and European levels of the Algerian decision.
The European Commission foreign affairs spokesperson, Nabila Massrali, said Algeria's decision was "extremely worrying," calling on Algiers to review it and work with Spain on solutions to their disagreement, without referring to the freezing of trade relations.
The European Commission's chief spokesperson, Eric Mamer, called Algeria to reverse this decision.
Meanwhile, Spanish Foreign Minister Joss Albares canceled a trip to the US to participate in the Summit of the Americas and arrived Friday in Brussels to discuss the issue with European Commission Vice President Valdis Dombrovskis.
Albares said, "Algeria is well known for being a trustworthy supplier (of gas) and has given guarantees from the highest level of its government" that the gas will keep flowing.
The minister said that the Spanish government is keen on maintaining the best relations with Algeria, like the rest of the neighboring countries.
Diplomatic efforts continue at the highest levels to contain the crisis between Madrid and Algeria. However, there is great concern among Spanish official circles about the unexpected levels this crisis has reached, according to a top Spanish official.
Spanish officials fear that Algeria will take the next step to limit its efforts to control illegal immigration, which crosses its territory towards Spain and the Balearic Islands in the coming weeks, knowing that it has declined 35 percent since the beginning of this year.
They don't believe Algeria would resort to cutting off gas supplies completely. However, the officials expect great difficulty in the ongoing negotiations to review prices, which have faltered for weeks.
Algeria's decision came after Spanish Prime Minister Pedro Sánchez told parliament on Wednesday that Western Sahara operating autonomously under Moroccan rule was "the most serious, realistic, and credible way" of resolving the dispute.
Spanish officials are surprised by Algeria's response to the Spanish position, compared to its reaction to the US stance, which favored Morocco, or the positions of France, Germany, and the Netherlands, which are identical to the Spanish position, or the UAE after it decided to open a consulate in Laayoune, Morocco.