Alarmed by rise in the incidents of bank robbery in Bihar, the state police has warned of penal action if its directive to switch off the mobile phones while entering banks in the state capital is not being strictly adhered to.

A decision to ban the use of the mobile phones was taken at a meeting of senior police officials with representatives of various nationalised and private banks on Monday, City Superintendent of Police Vikas Vaibhav said on Tuesday.

Now closed-circuit cameras would be installed at the main entrance of the banks besides at the cash counters and the strongrooms, he said.

"The bankers have been asked to make the people aware of the new directive through banners and posters," he said.

The ban was being imposed with investigations revealing that in most of the cases of bank robbery, the criminals used their cell phones, he said.

Henceforward, a police officer with a constable would escort the bank staff carrying cash from one branch to another on a two-wheeler regardless of whether the amount was big or small, Vaibhav said.

Armed criminals had recently looted Rs 50 lakh from bankers going to deposit the amount in the chest of the Punjab National Bank at Patrakarnagar in Patna and Rs 38 lakh of the State Bank of Bikaner being brought here from Muzaffarpur for deposit near Sarai railway crossing in Vaishali district.

In another incident, Rs 22 lakh was looted from the United Bank of India branch in Samastipur last month.