By Bart Biesemans

BRUSSELS (Reuters) -The exiled former leader of Catalonia, wanted for attempting the region's secession from Spain, laid out tough conditions for his party's support in parliament for the Socialist acting prime minister to stay in power following July's election.

Acting Prime Minister Pedro Sanchez would need the seven lawmakers in Carles Puigdemont's Junts per Catalunya party if he gets a shot at forming a government.

However, the Socialists said his conditions, including an amnesty for separatists, were far from what they would accept. An analyst said any agreement looked unlikely.

Speaking in Brussels, Puigdemont called on Spain to respect the Catalan independence movement's legitimacy and abandon judicial actions against it.

"We are prepared for elections but also for negotiations which could end with a historic agreement," Puigdemont said. "We have not endured all these years just to save a legislature."

Acting government spokesperson Isabel Rodriguez reiterated that the Socialists would not do anything that broke constitutional bounds.

"A world separates us from those positions," Rodriguez told reporters of Puigdemont's conditions. "Our framework is the one that the prime minister expressed with absolute forcefulness yesterday: We have a tool, dialogue; a framework, the constitution; and an objective: coexistence."

Alberto Nunez Feijoo, whose conservative People's Party (PP) won the most votes on July 23, will take the first stab at an investiture vote on Sept. 27, but his chances of winning are seen as slim since the PP opposes any concessions to separatists.

If Feijoo fails, it will fall on Sanchez to see if he can muster support, seen as impossible without Puigdemont's party.

Puigdemont, who lives in self-imposed exile in Belgium since leading the failed push to split Catalonia from Spain in 2017, said parliament would need to draw up legislation granting an amnesty for supporters of Catalan independence.

He also argued that an independence referendum would be legal and democratic and said all that was missing was the "political will" to make it happen.

But he stopped short of insisting on a vote as a condition for sitting down to negotiate. Puigdemont's regional government held a referendum on independence in Catalonia despite a ruling by Spain's constitutional court that it was illegal.

Drawing up an amnesty law before the formation of a new government would be impossible and makes an agreement unlikely, said Oriol Bartomeus, a professor at the Autonomous University of Barcelona.

"Puigdemont has left the PSOE no room to manoeuvre. He has come to say two things, the first is: 'here are my conditions' and the second: 'I am in charge'," Bartomeus said.

Feijoo said he had secured support from the hard-right Vox party that would allow the PP to govern as a minority. He said he was considering cancelling a planned meeting with Junts following Puigdemont's comments.

(Reporting by Bart Biesemans in Brussels, Inti Landauro and Belén Carreño in Madrid; Additional reporting by Emma Pinedo; Writing by David Latona and Charlie Devereux; Editing by Andrei Khalip, Peter Graff and Alison Williams)