ISLAMABAD, March 12 (Xinhua) -- A group of armed men opened fire on a passenger train in Pakistan's southwest Balochistan province on Tuesday, injuring several while many passengers were being held hostage, said official sources.

The Jaffar Express train with over 450 passengers onboard was heading from the country's southwest Quetta city to northwest Peshawar when the militants launched the attack in Kacchi district of Balochistan province, Muhammad Kashif, a senior official of Pakistan Railways, told Xinhua.

He said that an emergency relief train has been dispatched to the site with essential supplies, adding that several trains on the route have also been stopped as precautionary measures.

While a security official told Xinhua on condition of anonymity that the security forces halted the relief train's movement due to the evolving situation.

"The attack occurred in a mountainous region where communication is severely restricted due to the lack of mobile service. Our last contact with the train driver indicated that an explosion hit the railway track, forcing the train to stop. Immediately after, the militants opened heavy fire, injuring the driver and several passengers," the official said.

The train left the provincial capital city of Quetta at about 9:00 a.m. local time (GMT 0400), and at least six gunmen opened fire on the train, Balochistan government spokesperson Shahid Rind said in a statement.

As the passenger train was attacked in a remote hilly area, it was difficult for security forces and rescue teams to reach the site, he added.

A senior police official of Balochistan police told Xinhua on condition of anonymity that law enforcement agencies are investigating the nature of the attack, saying a possible terrorist act cannot be ruled out based on preliminary investigations.

A full-scale security operation is underway to rescue the passengers and ensure their complete safety, he added.

Following the incident, security forces and rescue teams rushed to the site.

Waseem Baig, media coordinator of the provincial health ministry of Balochistan, told Xinhua that an emergency has been declared at government hospitals in Quetta and some districts of the province after the attack.

All the consultants, doctors, pharmacists, staff nurses and paramedical staff have been summoned to the hospitals, he added.

Pakistani Interior Minister Mohsin Naqvi condemned the incident, saying the beasts that fire on innocent passengers do not deserve any concessions.

The proscribed terrorist outfit Balochistan Liberation Army (BLA) claimed responsibility for the attack in a statement on a social media platform, while Pakistani officials have not confirmed it.