The police on Wednesday raised a terror alert across Nellore district after information from their counterparts and intelligence agencies in Tamil Nadu that five activists of the Students Islamic Movement of India have entered Andhra Pradesh.

Security has since been tightened around Sriharikota and Sri City while police intensified patrolling at all places, particularly in the vicinity of the Satish Dhawan Space Centre.

The police have taken up frisking and have been checking vehicles at various places including the inter-State borders to trace the suspects, who are wanted in a bomb blast that took place in Chennai. Their names and photographs have been released by the T.N. police.

Checking has also been undertaken in neighbouring Chittoor district where some terrorists of another banned outfit had been arrested in 2014. A close watch has been kept in the coastal areas across the region.