Police in India have issued sketches of two men they believe got off a train to Pakistan just moments before it was hit by a deadly bombing on Sunday night.
The police say they have recovered bottles with kerosene from the train
The men got off the train "15 minutes" before the blast, the police said.
At least 67 people were killed when explosives started a fire on two carriages of the Delhi-Lahore train.
Pakistan's foreign minister has arrived in Delhi for scheduled peace talks. He has vowed that the attack will not undermine peace efforts with India.
Mr Kasuri is expected to visit some of the victims of the attack who are being treated in hospital in Delhi.
Ahead of his arrival, Mr Kasuri noted the attack was timed to coincide with his visit.
He said the bombing should "hasten the peace process".
"The governments of India and Pakistan should not allow the perpetrators of this incident to achieve their objectives."
It is not clear who was behind the attack on the Friendship Express near Panipat, 80km (50 miles) from Delhi, and no group has admitted carrying it out.
Haryana state police official Sharad Kumar told reporters that the two men police want to question boarded the train in Delhi and began an argument with the conductor, saying that they were on a wrong train.
"These people got down, and the blasts happened 15 minutes later," Mr Kumar said.
However, it is not known how the two men got off the speeding train, which had only slowed down after the driver was alerted that there was fire in two carriages.
The sketches of the men were based on details from 12 of the injured passengers.
Witnesses said they saw people screaming and struggling to get out of the fire-stricken carriages, hampered by bars on the windows.
"We couldn't save anyone. They were screaming inside but no-one could get out," rescue worker Rajinder Prasad said.
Mr Kumar said the police had recovered 14 plastic bottles "filled with kerosene", a suitcase and plastic digital timers from the site of the blasts.
One person has been detained in connection with the attack, Railway Minister Lalu Prasad Yadav said.
Most of those killed in on the train were Pakistanis.
By Tuesday afternoon 16 bodies, 12 of them Pakistanis and four Indians, had been identified at the Panipat government hospital, officials said.
BBC correspondents say about 20 of the bodies are so badly damaged that DNA analysis will be needed to identify them.
Rajbir Singh said he had identified his uncle Swaran by his missing toe.
"He's had one toe missing since he was a child. But we haven't told the women in the family yet," he told the BBC.
The twice-weekly train service, one of only two rail links between India and Pakistan, was restarted in 2004 after a two-year gap as part of the peace process between the two countries.
The BBC's Geeta Pandey in Delhi says the cautious response by the two governments - and the lack of finger-pointing - is being seen as a positive sign.
Indian police isay they want to question these two men
The fact that both sides suffered losses in the attack could be a catalyst for them joining hands and working together, our correspondent says.
Mr Kasuri will meet his Indian counterpart Pranab Mukherjee during his visit.
The sides say they will sign an agreement on reducing the risk of nuclear accidents.
The talks have been going on for three years, but have made little headway on key issues such as the dispute over Kashmir.