Compartments of Samjhauta Express burn after the explosions as the Samjhauta Express passed through Panipat.
India and Pakistan have vowed that explosions on board an Indian passenger train that killed at least 67 people will not derail the peace process between the two nations.
Most of the victims of the twin blasts early Monday on the New Delhi-Lahore train were Pakistani citizens, according to India's home minister. Twelve other people were injured.
Pakistani President Pervez Musharraf condemned the explosions as an act of terrorism, and said the attack would harden his resolve to pursue the peace process.
"The president underscored the need for the leadership of Pakistan and India to move forward undeterred in the quest for dispute resolution and lasting peace in the region," a government statement said, according to The Associated Press.
"He said that we will not allow elements which want to sabotage the ongoing peace process (to) succeed in their nefarious designs," it said.
Indian Home Secretary V.K. Dugal agreed, saying: "This is an act of sabotage. This was done to create a type of wedge. We won't allow this to come into the way of the peace process."
The pair of explosions happened in two passenger coaches as the Samjhauta Express passed through Panipat, about 80 kilometers (50 miles) north of New Delhi, said Northern Rail spokesman Rakesh Saxena.
The Samjhauta Express -- which translates as "Friendship Express" -- runs between India and Pakistan and was established several years ago as officials from the two countries worked to improve relations.
India and Pakistan, now both nuclear powers, have fought three wars since partition in 1947 following independence from Britain, two of them over the disputed region of Kashmir.
Dugal blamed the high death toll on the early hour of the blasts, saying many people were asleep on the train. Most of the people who died were burnt to death.
Residents living near the tracks rushed to the scene of the blast with buckets of water, and the blaze was eventually extinguished when fire trucks arrived, AP reported.
Hours later, authorities detached the burned cars, and the rest of the train continued on to the India-Pakistan border, according to AP.
Saxena said three unexploded bombs were found near the train tracks. There were 610 passengers on the train which originated in New Delhi, he said.
Dugal told CNN: "It now appears they were petrol-based devices."
The incident came as Pakistani Foreign Minister Khursheed Kasuri was due in New Delhi on Tuesday for talks with Indian leaders on the peace process between the two nations.
Aslam said Kasuri's trip would still take place.
"We have a very strong position that terrorist acts of this nature should not in anyway impede the peace process," she said. "This is something on which the two countries have agreed, at the highest level."
"We have strongly condemned this despicable act," Pakistani Foreign Ministry spokeswoman Tasnim Aslam said from Islamabad in a CNN interview.
"We expect the Indian government to conduct thorough investigations into these terrorist attacks and we hope that the results of these investigation will be shared with us and those responsible will be punished."