PHAGWARA: Two letters threatening that terror group Lashkar-e-Taiba(LeT) will blow up key temples in Punjab and Himachal Pradesh on June 5 to avenge the killing of al Qaeda chief Osama bin Laden were received by police here. One letter warns Hindus against undertaking pilgrimage to Amarnath cave and Mata Vaishno Devi shrines in J&K.