MADRID (Reuters) - Spain's influential El Pais newspaper withdrew what it said was "false photo of Hugo Chavez" that it had published in its on-line and print editions on Thursday.

Venezuelan President Chavez has cancer and has been under medical treatment in Cuba where he underwent surgery in December. He has not been seen publicly for six weeks.

The grainy photo that El Pais originally splashed on its front page, billed as a global exclusive, portrayed the head of a man lying down with a breathing tube in his mouth.

El Pais, one of the biggest Spanish-language publications in the world and an institution both in Spain and in Latin America, said in a brief on-line statement that it had withdrawn the photo after ascertaining that the image was not of Chavez.

Venezuelan political opposition leaders have criticized government secrecy over Chavez's condition while his supporters have accused foreign media of being in league with the opposition to spread rumours that the president's medical condition is worse than it is.

"El Pais apologises to its readers for the damage caused. The newspaper has opened an investigation to determine the circumstances of what happened and the errors that were committed in the verification of the photo," the newspaper said in the statement.

The photograph was on the paper's website for half an hour and also appeared in early editions of the print version of the paper, before the company stopped the presses and changed its front page, the company said.

(Editing by Jon Boyle)

• Travel Picks: Top 10 golf resorts around the world
• Chinese premier criticizes EU move on trade measures
• Justice Department opposes AMR's $20 million severance for CEO Horton
• News Corp to take charge of up to $1.4 billion this quarter
• Wall Street Week Ahead: Investors look for signs in the rally's break
• Unhappy with how your fave series is faring? Amazon gives you a say
• Visa, Mastercard ask U.S. court to declare card fees are lawful
• Wall Street posts first weekly loss since mid-April on Fed angst
• IMF's Lagarde escapes formal investigation in court
• Politics of development pays dividend
• A thematic play seen
• Sarawak counters hogging the limelight
• Getting GST acceptance will be tough
• A yen for the unloved dollar standard
• Bitten by the music bug

• French soldier stabbed on patrol in Paris
• Thousands run final mile of Boston Marathon as memorial
• Trio arrested over London soldier murder

• Sweet revenge as Froch defeats Kessler
• Pandelela-Mun Yee and Yan Yee-Jun Hoong bag bronze medals in Mexico
• World No. 1 Nicol sinks Waters to reach British Open final
• China confident of sweeping aside their final opponents
• Koreans in the final despite Dong-keun’s loss
• Macdonald and Marques share the lead
• McIlroy among big names who miss the cut as Molinari leads
• Kuchar leads in weather-hit second round
• Two tied at the top as rain stops play in the Bahamas
• Nico Rosberg revels in the rain as Mercedes stamp their mark
• Whitmarsh: McLaren’s hopes were too high this season
• Affendi brushes off hand injury to win CP130 race in Terengganu
• Hafizh needs to step up a gear after coming in fifth
• Vignesa right on track to retain GT Open title
• Dragons’ Melton confident of getting the better of Pringle in Game 2

• Please wait.

• Give birth naturally, women urged
• Too blessed to be stressed
• It takes nearly 72 hours to get a new polycarbonate passport now
• Indian warships visit Malaysian waters
• ‘Harry Potter Wong’ casts his spell
• Theme parks and long holiday help fill Johor hotel rooms
• Housewife extorted over nude pics
• Exemplary educators
• The Wall Street Journal: Anwar asked Jusuf to broker deal over GE13
• Weighing the options