The United Arab Emirates outlined plans Sunday to block BlackBerry e-mail, messaging and Web browsing services in a crackdown that could jeopardize efforts to establish the country as an international business hub.

The government cited a potential security threat because encrypted data sent on the devices is moved abroad, where it cannot be monitored for illegal activity. But the decision — quickly followed by a similar move in Saudi Arabia — raises questions about whether the conservative Gulf nations are trying to further control content they deem politically or morally objectionable.