Separatist rebels have set off two more explosions in India's north-eastern district of Assam, derailing a goods train and cutting off the region's rail link with the rest of the country, just a few hours after it was restored.

North-eastern railway spokesman Robin Kalita said a powerful explosion derailed a goods train at Kokrajhar early on Monday.

The driver, his assistant and three police guards were seriously injured.

Later, another explosion damaged a nearby rail bridge, just before the super-fast Rajdhani express from Delhi was to cross it on the way to Assam's capital, Guwahati.

Mr Kalita said the rail link between the north-eastern region and the rest of the country has been totally disrupted as a result of these explosions, a few hours after it was restored on Sunday night.

He said the north-eastern railway has now decided not to run any trains at night, even after the rail link was restored, until the rebel boycott of Indian independence day celebration on 15 August were over.

They said five local trains within Assam have also been suspended until that date.

Intelligence officials link the sudden rise in the bombing of rail tracks and road bridges in Assam to a call given by six rebel groups in north-east India to boycott the Indian independence day celebrations.

They say they suspect the involvement of the outlawed National Democratic Front of Bodoland or the NDFB in the bombing.

On Saturday, another such explosion damaged a rail bridge just before an express train from Delhi was to cross over it.

The bridge was repaired late on Sunday and trains started running again, but only for about six hours before the explosion early on Monday.

The road link to the region also remains disrupted after an explosion on Sunday damaged a bridge on the national highway that links the north-east with the rest of the country.