By Belén Carreño and Inti Landauro MADRID (Reuters) -Spain said it will firmly defend its national interests following Algeria’s decision to suspend a 20-year-old treaty of friendship and cooperation and ban all non-gas trade, a move that also alarmed EU officials. Spain was also monitoring gas flows from Algeria, its second-largest supplier after the United States, but these were unaffected by the diplomatic rift over Madrid’s stance on the disputed territory of Western Sahara, Foreign Minister Jose Manuel Albares said on Thursday. Albares will travel to Brussels on Friday to discuss the cris…