India and Pakistan have condemned a train bombing that killed at least 66 people as an act of terrorism aimed at disrupting their peace process.
The "Friendship Express" restarted in 2004 after a two-year gap
Pakistan's President Pervez Musharraf vowed the attack would stiffen their resolve to reach a sustainable peace.
The train, running from Delhi to Lahore in Pakistan, was hit by two blasts at about midnight (1830 GMT Sunday) near Panipat, 80km (50 miles) from Delhi.
The ensuing fire swept through two carriages of the "Friendship Express".
It is thought three-quarters of the 750 people on the train were Pakistanis, as were most of the dead.
'Anguish and grief'
President Musharraf said the attack was a heinous crime.
"Such wanton acts of terrorism will only serve to further strengthen our resolve to attain the mutually desired objective of sustainable peace," he said.
Indian Prime Minister Manmohan Singh expressed "anguish and grief" and vowed the culprits would be caught.
Pakistan's Foreign Minister Khurshid Kasuri said he would go ahead with a planned visit to India on Tuesday.
The reaction from both governments suggests the prime suspects might be groups such as Lashkar-e-Toiba and Jaish-e-Mohammad - the main Islamic militant groups who have been blamed for many high-profile bombings, says the BBC's Jill McGivering.
Recent attacks on Delhi, Mumbai and Varanasi, for example, seemed designed to damage India's image abroad and stoke anti-Pakistan feeling inside India.
But the fact that so many of the dead on the train were Pakistani Muslims may indicate that the devices were intended for a different target, or exploded prematurely, she says.
Initial investigations suggest explosives in suitcases ignited bottles of paraffin to start a blaze.
Anxious families gathered at Delhi's main rail station for information
Witnesses said they saw people screaming and struggling to get out of the fire-stricken carriages.
The BBC's Soutik Biswas, at the scene, said the heat of the flames had peeled the blue paint off the coaches, and oil and cinders covered the tracks.
Shiv Ram, a police railway constable, was one of the first officials on the scene.
"The coaches were totally engulfed in flames. I brought out three charred women - I could only recognise them as women because they were wearing bangles," he said.
Many train windows in India have bars on them for security reasons.
A rescuer, Rajinder Prasad, said: "We couldn't save anyone. They were screaming inside but no-one could get out."
A doctor in Panipat, Ved Gupta, said: "It's very difficult to say who the victims were. Most of the bodies were charred beyond recognition."
Relatives who gathered at Delhi station were given only a list of 13 injured and one identified body.
The burnt-out carriages were moved to a railway siding a couple of kilometres away for forensic examination.
Service suspended after 2001 Delhi parliament attack
Restarted in January 2004 as part of peace moves
Connects Delhi and Lahore, via Atari
Runs twice a week
One of a series of measures easing travel restrictions
The rest of the train continued on its journey to the border station of Attari where passengers switched to another train to travel on to Lahore.
The Indian High Commission in Islamabad said arrangements were being made to process visas immediately for Pakistanis who had relatives on the train and wished to go to India.
The twice-weekly service from the Indian capital to Lahore was restarted in 2004 after a two-year gap as part of the peace process between the two countries.