Rail links between India's north-eastern states and the rest of the country have been cut off by a powerful explosion.

The blast derailed a goods train and damaged a long stretch of the rail tracks in India's north-eastern state of Assam early on Sunday.

No-one has claimed responsibility for the explosion but police said they suspected the involvement of either of the two major separatist groups active in Assam.

Rail officials said the blast could have caused a major disaster as three passenger trains were due to cross the line around that time.

The explosion happened between Rangiya and Ghagrapur railway stations and derailed 12 carriages of the goods train.

North-Eastern Frontier Railways spokesman, Robin Kalita, told the BBC that the blast created a crater five metres deep and blew off nearly 200 metres of the rail track.

Repairs

Workmen are expected to take at least take two days to restore the tracks and until then the north-east Indian states will remain cut off.

Assam police officials said either of the state's two major separatist groups could be responsible.

The two groups, the United Liberation Front of Assam, or the ULFA, and the National Democratic Front of Bodoland, or the NDFB, have targeted rail communications and oil installations in the state every year on the eve of India's Independence Day celebrations on 15 August.

The ULFA is fighting for an independent Assam, while the NDFB wants an independent homeland for the Bodo tribes.

BBC correspondent Subir Bhaumik, reporting from Calcutta, says both are active in the area where the explosion took place.