Fourteen passengers were killed and about 50 wounded on Tuesday when militants bombed a train in Pakistan's Baluchistan province, hospital sources and officials said.
The blast came a day after Pakistani security forces said they had killed 30 separatist militants in one of the biggest clashes in months in the gas-rich province.
The separatist United Baluch Army claimed responsibility, saying in a text message to Reuters the bombing was retaliation for the raids by security forces.
The bomb went off on the Rawalpindi-bound Jaffar Express in a carriage reserved for men, in the town of Sibi, 120 km (75 miles) southeast of the provincial capital of Quetta.
"Fire engulfed the (carriage) following the blast causing most of the deaths," said a rescue worker. Railways Minister Khawaja Saad Rafique confirmed the death toll.
The low-level separatist insurgency in Baluchistan is one of the chronic security problems undermining stability in nuclear-armed Pakistan.
The separatists accuse the government of stripping the province's natural resources and leaving its people mired in poverty. They say government-backed death squads routinely abduct, torture and execute ethnic Baluch, accusations echoed by human rights campaigners.
The security forces deny violating human rights.
Insurgents have also targeted civilians, especially Pakistanis from other ethnic groups who have settled in Baluchistan.
The government tightly controls access to the province and it is difficult for foreign journalists to get permission to travel there.
As well as the separatists, Islamist militants operate in Baluchistan, which shares borders with Iran and Afghanistan.