OVIEDO, Spain 

Spanish King Felipe VI kicked off a first round of talks with political groups on Monday, before having to decide who he will nominate to be the country's next prime minister. 

It is an unprecedented situation for the king: both Spain's current Prime Minister Pedro Sanchez and Popular Party leader Alberto Nunez Feijoo say they can muster the parliamentary majority needed to form a government.

After July's inconclusive election, both the right and left-wing blocs fell short of the required majority. This has forced both sides to negotiate with regional parties that have their own demands.

And despite both politicians having asked the king to nominate them to form a government, they both lack outright political support. This puts the king in a difficult political situation since Spain's constitution does not specify who should be nominated when neither is guaranteed to meet the requirements.

On Monday morning, the king met with the smallest regional parties that could be swayed.

The Union of the People of Navarro (UPN) party said it would back Feijoo. Later, the Canary Island Coalition party said it is open to backing Feijoo as well, or Sanchez if the left wing promised to meet its demands.

Aitor Esteban, leader of the Basque party PNV, who is also meeting with the king on Monday, said it is too early for the king to pick a candidate.

Last week, the Socialist Party won the majority support in parliament to elect a speaker, but Esteban and other regionalist parties have emphasized that this does not guarantee they will back a Sanchez-led government.

But given the other parties' political stances, the Catalan separatist parties appear to have emerged as the ultimate kingmakers. And, given their opposition to the monarchy, they are refusing to meet with Felipe VI, leaving the king in the dark about their intentions.

Behind closed doors, they are negotiating with Spain's left-wing bloc, demanding hard-to-grant concessions like amnesty for Carles Puigdemont and other exiled Catalan leaders who led the 2017 independence attempt. Their leaders are much more likely to reach an agreement with Sanchez, but they could also refuse to back anyone and drive the country to fresh national elections.

Tensions are also emerging within the right-wing bloc, which seems to have a dwindling probability of being able to form a government.

Before meeting with the king on Tuesday, the far-right party Vox on Monday refused to guarantee support for the Popular Party without a public explanation for why it gave Vox the cold shoulder when voting on bureaucratic positions in Spain's parliament last week.

Felipe VI will finish meeting with willing political parties on Tuesday and could make his decision then. But he may also wait until the picture becomes clearer before deciding who he believes has a better chance of leading Spain.