India has blocked services to at least 20 million cell phones because of concerns about security.

The government took the action Tuesday, which was the deadline for owners of the inexpensive, mostly Chinese-made cell phones to purchase additional equipment or face the loss of phone services.

India says the targeted phones lack International Mobile Equipment Identification (IMEI) - a 15 digit number that allows calls to be traced.  Indian intelligence agencies have warned that militants could use the untraceable phones to launch attacks.

Consumers flocked to stores Monday to purchase the equipment needed to install the IMEI number on their phones. 

In late October, the government banned the use of pre-paid mobile phone connections in the volatile Indian-controlled part of Kashmir.  The government also cited security concerns for the ban. 

Some information for this report was provided by AFP and Reuters.