The results from Sunday's vote left neither the left nor right bloc with an easy path to form a government.
Prime Minister Pedro Sanchez' Socialists have more options but face potentially unpalatable demands from Catalan separatist parties.
Those could include insistence on an independence referendum, triggering the kind of political chaos seen in 2017 when Catalonia last tried to break from Spain.
Sanchez could win over left-wing separatist party Esquerra Republicana de Catalunya (ERC), as he did to form a minority government in 2019.
The Socialists, which oppose independence and any vote on the issue, may have a hard time accepting such a demand.
Persons:
Pedro Sanchez, Begona Gomez, applauds, gridlock, Ignacio Jurado, Vox, Sumar, Sanchez, Esquerra, Junts, Miriam Nogueras, Carles Puigdemont, Ignacio Torreblanca, Charlie Devereux, Belen Carreno, Joan Faus, Cynthia Osterman
Organizations:
Socialist, REUTERS, Carlos III University, People's Party, Socialists, PSOE, ERC, Congress, Spanish, European Council, Foreign Relations, Thomson
Locations:
Madrid, Spain, Catalan, MADRID, Catalonia, Belgium, Basque, Barcelona