In a major Naxal attack, 12 CRPF personnel were today killed and 28 others injured when naxals triggered a landmine blast in Gadchiroli district of Maharashtra. A total of 40 troops were travelling in a bus from Pushtola to Gatta, about 4 kms from here, for an operational duty when at around 1130 hours the blast took place, killing 12 of them.