Fans at the concert called for Haidar's release
Spanish artists, singers and actors have staged a concert in support of a Western Sahara activist on hunger strike on the Spanish island Lanzarote.
Aminatou Haidar, nicknamed the "Gandhi of Sahara" after seeking independence for the disputed region, was refused re-entry to Morocco on 15 November.
Morocco controls the Western Sahara but many there want self-determination.
Film director Pedro Almodovar was among 1,000 people at a concert near Madrid calling on Morocco to allow her back.
Dozens of Spanish singers and artists performed under a massive image of Ms Haidar, who wants to return to her home in the Western Saharan city of Laayoune.
Ms Haidar remains camped in Lanzarote's airport
The hit Spanish singer Dani Macaco joined the concert in Madrid - to pressure his government to intervene.
"They are in big trouble. If she dies the government will be in bigger trouble. That is what we trying to do - to use our popularity to try make more pressure - and we hope that she lives," he said.
Moroccan officials had confiscated Ms Haidar's passport when, on returning from Lanzarote after collecting a prize, she refused to state her citizenship as Moroccan.
On Saturday Spain offered her Spanish nationality in an attempt to break the deadlock.
Spanish foreign minister Miguel Angel Moratinos said: "In order to show we're prepared to do whatever is necessary, we've made an exception on humanitarian grounds.
"We'll try to get her Spanish nationality and a Spanish passport as quickly as possible."
But Ms Haidar, who is camped outside Lanzarote airport, has demanded her original passport back and refuses to ask for another one.
She has vowed to carry on refusing food and said she is prepared to die if she cannot return home.
On 17 November Ms Haidar was told to appear in court after a public order complaint by the airport where she remains camped.
Supporters say Ms Haidar, who won the Robert F Kennedy Human Rights Award last year, is in a weak condition.
Morocco annexed Western Sahara in 1975 after Spain withdrew from the territory.