Indian troops deployed to quell ethnic violence in the northeastern state of Assam are under orders to shoot suspected rioters on sight amid clashes that have killed at least 22 people.

Local officials called for even more troop reinforcements Tuesday after fresh fighting erupted overnight, with more homes burned by rival mobs. In one of the latest incidents, a group of hundreds attacked an express train passing through the region early Tuesday.

More than 40,000 people have fled their homes since clashes between ethnic Bodo tribespeople and Muslim settlers began Friday. The New Delhi government has opened shelters for those displaced.

Animosity and accusations of land-stealing have long simmered in the region between members of the ethnic Bodo community and the thousands of mostly Bengali Muslim settlers, many of whom came from the former East Pakistan before it became Bangladesh in 1971.