Bhubaneswar, Aug 12 - Security has been beefed up at a National Aluminium Co Ltd (NALCO) mine in Orissa following a Maoist threat, a senior company official said Wednesday. The rebels had attacked the mine earlier April 12 and killed 10 security personnel.

Patrolling by the security personals has been intensified in and around the mine at Panchpatmali hills in Koraput district that feeds the company's refinery at Damanjodi town located nearby.

'We have beefed up security after we recently received a letter allegedly sent by Communist Party of India (Maoist),' P.K. Mohapatra, the head of the Damanjodi refinery and mine, told IANS by phone.

The one-page letter written in Telugu has asked the mine and refinery authorities to carry out peripheral development around the mine and regularize 2,000 contract workers.

The letter has warned that the authorities would be held responsible if they do not carry out the instructions in a month's time.