India has sent formal notices to the country`s mobile operators telling them they must have equipment to monitor Blackberry services by 31 August.

The move will increase pressure on Blackberry maker Research in Motion (RIM) to allow Indian security agencies access to encrypted messages.

Tata Teleservices told BBC News that the letter said it must "ensure that Legal Intervention (LI) capability is put in place" by the end of the month.

India, along with many other countries, believes the device and the Blackberry infrastructure are a threat to national security. Blackberry handsets automatically scramble messages and send them to servers in Canada and other countries.

Authorities have said they want access to these messages and the keys to decrypt them to counter terrorism and criminal activity.

The row in India is the latest in a long-running dispute between RIM and international governments.

The United Arab Emirates was the first country to propose a block on the devices, followed by a raft of others including Lebanon, Algeria, Saudi Arabia and Kuwait.

BDST: 1515 HRS, 18 August 2010