Five people were killed and four others were wounded when a bomb hit a passenger train in the north-eastern part of India, in the Assam state on Thursday.

According to Indian Railway spokesman T. Rabha, the New Delhi-bound Rajdhani Express line left from the eastern town of Dibrugarh and just as it past a station near Chungajan, at 1 a.m., the explosion went off, at 168 miles east of state capital Guwahati, Houston Chronicle reports.  

The bomb that was planted on the tracks exploded as soon as the train passed the section.

Rabha said: "A car near the luggage car took the whole impact of the blast before dawn Thursday. Five passengers were killed and four others wounded."

After the authorities repaired the tracks and inspected it, the train continued its journey.

All the victims were all-Hindi-speaking migrant workers. Local reports believe that the attack was provoked by Assam’s separatist groups, which have been targeting the migrants in the past, DPA informs.

The Golaghat police chief P.C. Haloi said: “The needle of suspicion is on two militants groups - the ULFA (United Liberation Front of Asom) and the ALNA (Adivasi National Liberation Army).”

Ever since 1979 the ULFA has been fighting for an independent Assamese homeland.

ALNA, an active group located in Golaghat and Karbi Anglong districts of eastern Assam, is fighting for tribal rights in the area.

P. Saloi, a police superintendent said: "We suspect the bomb was planted inside the train from early examinations, but we cannot conclude for sure just now.”

The Rajdhani Express is a popular air-conditioned train that is connecting the northeast of India with the capital. Its full capacity is off 900 passengers.

The train network in India is often targeted by terrorists and militants.

The Samjhauta Express between India and Pakistan was attacked earlier this year, when 68 passengers were killed and 60 were wounded.