Quetta - At least seven passengers were killed and 20 wounded after two explosions targeted a passenger train in Machh city of Balochistan on Friday.

The twin blasts hit the Rawalpindi-bound Jaffar Express as it passed near a village of Machh, about 65km southeast of Quetta.

"The explosions damaged two passenger carriages and seven of the travellers were killed," Imtiaz Ahmad, a senior Pakistan Railways official, told reporters, updating an earlier toll of three deaths.

According to a private TV channel, the first bomb targeting Jaffar Express left eight people injured while the second blast was occurred when rescue operation was underway.

The police, hospital sources and senior officials of Pakistan Railways confirmed death of seven passengers and injuries to 20 others in the twin blasts. "Seven bodies were placed at hospital and the injured passengers were brought to Quetta from the scene," they said.

"Jaffar Express left Quetta Railway Station at around 9 am for Rawalpindi and after few minutes stay at Machh Railway Station, it was moving on to Sibi when it was targeted by terrorists in an area between Machh and Aab-e-Gum, some seven kilometres off Machh town," an official said.

The locomotive of the train was also partially damaged. The bogies No 3 and 5 were badly damaged as twin bombs ripped through them.

The rescue teams including Army Aviation helicopter rushed to the scene and 10 injured were brought to Combined Military Hospital Quetta by Army helicopter and 10 others were also shifted to Quetta by road. According to doctors, condition of some injured was critical.

According to bomb disposal squad, five kg explosives were used in the blasts which had nature of improvised explosive device (IED).

The attack was claimed by the Baloch Liberation Army, according to AFP. A spokesman for the group said the bombing had targeted "military personnel who travel to Rawalpindi by this train".

Kashif Akhtar, a senior railways official, told Reuters that security forces foiled a similar attack on Thursday as an attacker laid explosives on a railway track near Quetta.

Railways Minister Khawaja Saad Rafique denounced the bombing as "an act of terrorism" and said authorities were still trying to determine how the bomb was planted on the train.

Talking to media in Islamabad, Saad Rafique said the department will hold proper inquiry into who had allowed the train to travel without security clearance. He also revealed that one suspect has been taken into custody.

"There was another blast after the first one with an interval of 20 minutes at the same spot," Hameed Gul, a senior railway official, told reporters.

The train service was restored between Quetta and other parts of the country after technical staff repaired the damaged portion of the track.

The Jaffar Express , which was targeted in the twin blasts, also continued its journey to Rawalpindi following clearance.

Earlier in January, two bogies of the Jaffar Express were partially damaged in an explosion near railway tracks in Mithri area of Balochistan's Sibi district. In June this year, suspected terrorists had blown up a portion of the railway track in Bakhtiarabad area of Bolan district.

Prime Minister Nawaz Sharif strongly condemned the attack on Jaffar Express near Machh. He expressed deep grief and sorrow over the loss of precious lives in the blasts.

The prime minister directed the authorities concerned to arrest the culprits and bring them to task immediately. He directed to provide the best medical treatment to those injured. He prayed for early recovery of the injured.

Balochistan Chief Minister Sanaullah Zehri also condemned the attack and directed the IGP to hold an inquiry and submit a report in this regard. He also directed the chief secretary to submit a report within 24 hours and install secret cameras at all railway stations and bus stops.

Earlier, one terrorist was killed in an exchange of fire with Frontier Corps (FC) in Dera Murad Jamali.

The officials were guarding the railway track when they spotted a suspicious man installing a bomb at the railway track. They chased him and killed him during an exchange of fire.

Improvised Explosive Device (IED) weighing 5kg, one sub-machine gun (SMG), detonator and wires were recovered from the terrorist.

The killed terrorist was identified as Zafar Bugti who is the local commander of a banned outfit.