As part of tightening security for Republic day celebrations, Central Industrial Security Force on Monday upgraded surveillance at the airport here, posting armed men on the open terrace of Domestic and International terminals.

Armed personnel will be on alert till month-end and they will keep watch on the recently constructed flyover located outside the airport as those travelling on it would have a full view of the airport, officials said.

The Centre had already warned of terrorists’ plans to hijack Indian aircraft operating between SAARC countries following which security had been beefed up at Chennai airport also, with entry of visitors banned till January 31.

Tamil Nadu, Chennai in particular, has already been brought under a security cover with vigil intensified on borders and coastal areas.

A 12,000 strong police force will guard the city on the occasion of Republic Day celebrations.