Any solution provided by Research in Motion, makers of BlackBerry smartphones, must pass through field trials to satisfy India's security concerns, a senior government source said on Friday.

RIM on Thursday offered to lead an industry forum to look at India's need to have lawful access to its encrypted mail and messenger in an effort to stave off the blocking of the popular service in the world's fastest growing telecoms market.

Executives of the Canadian firm will meet government officials for a second day on Friday in last-ditch negotiations aimed at finding a solution to India's desire to access the encrypted data that security agencies fear could be misused to launch attacks or create political instability.

RIM faces an August 31 deadline to give authorities the means to track and read BlackBerry Enterprise email. The government has said it will take a final decision on Monday.

Indian officials say nothing short of a solution which will give them access to email in a readable format will satisfy them.

We will only accept a solution which will enable us lawful interception of BlackBerry services in the interest of national security, the source told Reuters.

The solution, if they come up with it, will have to go through field trials and satisfy our technical experts.

RIM said it was willing to lead an industry forum focused on supporting the lawful access needs of law enforcement agencies while preserving the information and security needs of corporations.

We have seen the statement, but the government's position does not change, the source said. We are hopeful they will come up with some solution.

A shutdown would affect about 1 million users in India out of a total 41 million BlackBerry users worldwide, allowing them to use the devices only for calls and Internet browsing.

RIM uses powerful codes to scramble, or encrypt, email messages as they travel between a BlackBerry device and a computer known as a BlackBerry Enterprise Server (BES) that is designed to secure those emails.

RIM has said BlackBerry security is based on a system where the customers create their own key and the company neither has a master key nor any back door to allow RIM or any third party to gain access to crucial corporate data.

India is one of a number of countries putting pressure on RIM, which has built the reputation of the BlackBerry, popular with business professionals and politicians, around confidentiality.

(Editing by Sugita Katyal)