An interior ministry spokesman said any terrorist link had been "completely ruled out", telling AFP: "Everything indicates that it was an accident, that the train derailed and was hurled against the walls of a tunnel."

 But the deadly accident gave Spanish commuters a grim reminder of the train bombings by Islamist militants that killed 191 people in Madrid in 2004.

 Regional transport chief Jose Ramon Garcia Anton warned that speculation about the cause of the crash would be premature until the train's black box recording was found.

 "We have to be prudent and wait for the enquiry to uncover the causes of the accident," he said.

 Monday's derailment happened at 1:00 pm (1100 GMT) as the train was between the Jesus and Plaza de Espana stations.

 In one of the worst metro accidents in the past 50 years, a fire brigade spokesman said that two carriages of the train had come off the rails in a tunnel.

 "It seems it was an accident that was apparently brought about by speed and a failure at the wheel level," said local deputy prefect Luis Felipe Martinez.

 "41 people are dead including the driver and ticket inspector," said Mikel Dominguez, security advisor to the city of Valencia.

 Of the 39 injured, 12 remained in hospital, he added, with two in "very critical" condition.

 "There was a collision, strange noises, then nothing," one of the train passengers told local radio. He managed to escape through a window as rescue workers turned up.

 Prime Minister Jose Luis Rodriguez Zapatero cut short a visit to India to travel to Valencia, officials said.

 "My thoughts are with the town of Valencia... and I express my condolences with the victims of this tragedy," he said in New Delhi.

 Zapatero was to attend a funeral service here late Tuesday.

 A passenger on board alerted emergency services at 1:03 pm (1103 GMT). Access to the area was sealed off and a security cordon installed.

 The accident happened as Valencia was filling up with visitors to the Roman Catholic Church's fifth World Family Meeting this week, which is due to be closed by Pope Benedict XVI at the weekend.

 The Vatican said the pope had been immediately informed and had prayed for the victims of the accident.

 "The Holy Father was immediately informed of the tragic accident in Valencia and has followed with pain and compassion the dramatic news coming out of the town," the Vatican said in a statement.

 "He has prayed for the victims, their families and all those affected by this terrible event."

 According to the Valencia metro website, the regional government-run company was distributing half-a-million passes to pilgrims and organisers of the event to permit them to travel freely on the system's four lines.

 The European Parliament observed a minute's silence following news of the accident, and the European Commission President Jose Manuel Barroso expressed his "solidarity with the people of Valencia".

 Technicians worked overnight on righting and removing the train wreckage.

 The victims' bodies were taken away for identification and a team of 15 psychologists rushed in to help the bereaved and traumatised.

 Some 500 people turned up searching for loved ones with no official victim list yet published.

 The same train line was the scene of a crash last September which left 35 people injured. The Valencia metro opened in 1988.

 The worst metro accident in recent history was in 1995 in Azerbaijan, when 290 people were killed and more than 270 injured after a fire on board a train between two stations in the capital Baku.

 A meeting scheduled Tuesday between the Basque branch of Spain's ruling Socialist Party and the banned political wing of the armed separatist movement ETA was cancelled following the Valencia disaster, Spanish media reported.

 The talks were set up after Zapatero said his government would open dialogue with ETA, three months after the movement declared a permanent ceasefire.

 ETA has been held responsible for the deaths of some 800 victims in its campaign of bombings and shootings for the independence of the Basque Country that began in 1968.

Agence France Presse