The Pentagon on Thursday cleared BlackBerry and Samsung mobile devices for use on Defense Department networks, a step toward opening up the military to a wide variety of technology equipment makers while still ensuring communications security.

Lieutenant Colonel Damien Pickart, a Pentagon spokesman, said the department cleared the use of BlackBerry 10 smart phones and BlackBerry PlayBook tablets using its Enterprise Service 10 system, as well as Samsung's Android Knox.

"This is a significant step towards establishing a multi-vendor environment that supports a variety of state-of-the-art devices and operating systems," Pickart said in a statement.

The Pentagon said on Wednesday it also expected to clear Apple mobile devices using the iOS 6 system at some point in early May.

The move to open up Defense Department networks is expected to set the stage for an intensified struggle for Pentagon customers among BlackBerry devices, Apple's iPhones or iPads and units using Google's Android platform such as Samsung Electronics' phones.

The Pentagon currently has some 600,000 users of smart phones, computer tablets and other mobile devices. The department has 470,000 BlackBerry users, 41,000 Apple users and 8,700 people with Android devices. Most Apple and Android systems are in pilot or test programs.

The move to open up the networks to a broader array of mobile devices is part of a Pentagon effort to ensure the military has access to the latest communications technology without locking itself in to a particular equipment vendor.

To ensure security, mobile devices and operating systems go through a security review process approved by the Defense Information Systems Agency. Once their Security Technical Implementation Guide - or STIG - is reviewed and approved, the devices can be used on the network.

Pickart said the decision on Thursday did not result in product orders. But it will enable user groups within the Pentagon to purchase the devices most appropriate for their work as the need arises.

"We are pleased to add Blackberry 10 and the Samsung Knox version of Android to our family of mobile devices supporting the Department of Defense," he said. "We look forward to additional vendors also participating in this process."