MADRID, Spain -- The leading Spanish newspaper El Pais withdrew and reprinted its Thursday edition after discovering that its front-page exclusive photograph supposedly showing ailing Venezuelan President Hugo Chavez being treated in Cuba was a fake.

The newspaper apologized to its readers for the mistake and said it was investigating how the photo made its way into the paper. The Venezuelan government announced that it would sue El Pais saying the image was grotesque and an offence to Chavez's dignity.

The poor-quality image showed the head of a man apparently on a hospital bed with tubes in his mouth.

El Pais had received the picture from an agency, Gtres Online, which declined to comment on the situation. The agency handles mainly entertainment and celebrity photos. The agency also offered the photo to The Associated Press and another Spanish newspaper, which both turned it down.

El Pais said it withdrew its Thursday edition and changed its website after it discovered the photograph was not of Chavez. The Venezuelan president has not been seen in public since before he underwent cancer surgery on Dec. 11 in Cuba.

The newspaper early Friday published details of the incident on its website, saying it will review its procedures. It said the agency Gtres Online had offered the newspaper the image on Wednesday morning through regular channels. The newspaper said that when it asked Gtres Online about the origin of the photo, "the agency said it come from a Cuban nurse through her sister, a resident in Spain."

El Pais prints some 340,000 copies daily. Many copies had already been distributed before the decision to reprint but the newspaper declined to say how many with the fake photograph had reached the streets.

El Pais said the photograph was on its online edition for 30 minutes before the error was discovered and the site changed.

Venezuelan Information Minister Ernesto Villegas denounced the photograph as a fake in a series of Twitter messages. He said the picture came from a video of another man and he circulated a link. That video, uploaded to YouTube in 2008, clearly shows another patient lying on a treatment table as doctors and nurses insert a tube into his throat.

"Would El Pais publish a similar photo of some European leader? Of its director? Yellow journalism valid if the victim is a South American revolutionary," Villegas said in one tweet.

Speaking at a news conference, Villegas read a statement strongly condemning the Spanish newspaper for publishing the image, saying the daily "violated journalistic ethics" and "created an international scandal."

Foreign Minister Elias Jaua said Thursday night in a telephone call broadcast on state television that the government instructed its ambassador in Spain, Bernardo Alvarez, to work with the attorney general in preparing the case.

The foreign minister said Vice-President Nicolas Maduro instructed officials "to take actions leading to a lawsuit against that daily for the acts that seriously offended the president's dignity."

Pedro J. Ramirez, editor of the Spanish paper El Mundo, said in tweets on Thursday that his paper was also offered the photo. However, he and other editors expressed reservations over whether it was genuine before announcing a unanimous decision to refuse it.

Santiago Lyon, AP vice-president and director of photography, said the AP turned down the agency's offer of exclusive rights to distribute the photo "because of serious concerns over medical privacy issues as well as the authenticity and provenance of the image."