India has sent a formal notice to mobile operators ordering them to ensure security agencies can monitor BlackBerry messages by the end of the month, companies said Tuesday.

The move rachets up pressure on the smartphone's Canadian makers Research in Motion (RIM) to satisfy a demand from the Indian home ministry for access to the heavily encrypted messaging service and corporate emails.

Telecom operators have a responsibility under Indian law to ensure security agencies can access all services carried on their networks.

"We have received a letter telling us to ensure legal intervention capability for BlackBerry services is in place by August 31," a spokesman for Tata Teleservices, one of India's leading mobile operators, told AFP.

"All the operators have received a letter," said an executive of another leading cellular firm, who declined to be identified.

India's home ministry said last week it would cut off the popular corporate email and messaging services unless RIM gave security agencies access by August 31. The move would affect about 1.1 million users.

The government has said RIM has promised to provide "technical solutions" for monitoring BlackBerry services.

The notices to the operators came amid reports citing unidentified government sources that RIM would offer partial access to BlackBerry's messaging services and was working on giving full access by the end of the year.

It was not immediately known whether such a compromise would satisfy New Delhi, which is battling insurgencies from Kashmir in the northwest to the far-flung northeast.

The government has raised fears that BlackBerry services could be used by militants. Islamic militants used mobiles to coordinate the 2008 Mumbai attacks that killed 166 people.