[5][6] In 1206, Muhammad bin Bakhtiyar Khalji planned to invade Tibet, in order to plunder the treasures of the Buddhist monasteries and gain control of Bengal's traditional trade route with South East Asia[7] for which he had to pass through Kamrup and Sikkim.
So he found a local guide belonging to a tribe named Mech who could show him a route through Bhutan, that could bypass Kamrud as the Islamic forces use to pronounce Kamrup.
But there was a uprising among the Tibetans who inflicted heavy casualties on Bhaktiyar's forces by carrying relentless guerrilla-style attack on the Turkish army.
The Rai of Kamrup allowed Bakhtiyar Khalji's army to advance unchecked into his kingdom, in order to draw him away from his base of operations.
He followed a scorched earth strategy, denying his enemy the opportunity to replenish their supplies and destroyed a bridge across the Teesta river[9] that Bakhtiyar Khalji's army had already crossed, thus cutting off their retreat.
He made stockades of phanjis or spiked bamboos and drew the whole surviving army of ten thousand into a gully and attacked them and mercilessly cut them down.
No reference to this expedition can be had from the Muslim chronicle Tabaquat-i-Nasiri except the following: The accursed Bartu (Britu), beneath whose sword above a hundred and twenty thousand Musalmans had attained martyrdom, he (Nasiruddin) overthrew and sent to hell.