The Pentagon will no longer retain an exclusive contract with Blackberry maker Research in Motion and has invited companies such as Apple to offer smart phones to its vast work force.

The move, announced Thursday, comes only days after another government agency, the US Immigration and Customs Enforcement agency, said it was dropping the Blackberry device altogether in favor of Apple's iPhone.

The Defense Department insisted it would still continue to work with Blackberry phones and that "large numbers of RIM devices" would remain in use among thousands of military personnel and civilians working for the Pentagon.

"DoD is not moving away from RIM and the use of Blackberry mobile devices," spokesman Lieutenant Damien Pickart said in an email.

The Pentagon, however, wants to establish a "multi-vendor environment" while still adhering to "strict security requirements," he added.

The US military and intelligence agencies have long preferred the Blackberry due to security concerns and had worried that Apple, Android and other smart phones lacked sufficient safeguards.

But the technology has advanced and Pentagon officials said innovative applications available on other smartphones could be useful for different units or offices.

"There's a lot more flash and bang with an Apple iPhone or an Android," said one defense official, who spoke on condition of anonymity.

The Canadian firm RIM has struggled to compete against the iPhone and devices that use Google's Android system.

The change at the Pentagon would likely be carried out as a pilot project in a particular unit or organization, the official said.

Questions remain, however, as to whether companies other than Blackberry can meet the strict encryption criteria employed by intelligence services within the Defense Department, including the eavesdropping National Security Agency.