Saudi Arabia has announced it will stop Blackberry services on 6 August, confirming fears the authorities would enforce a block before the end of the month.
The Saudi telecoms authority said the services did not conform to regulatory requirements, without giving any details.
The announcement comes just days after telecoms authorities in the United Arab Emirates (UAE) said it would block Blackberry services from 11 October.
The Saudi and UAE authorities are concerned about the secrecy afforded by Blackberry's encrypted messaging application.
India has raised similar security concerns that encrypted data could be used to coordinate acts against the state.
But Blackberry maker Research In Motion (RIM) says there is no way for RIM or any third party to access the encrypted data.
"RIM cannot accommodate any request for a copy of a customer's encryption key, since at no time does RIM, or any wireless network operator or any third party, ever possess a copy of the key," the company said.
"RIM has spent over a decade building a very strong security architecture to meet our enterprise customers' strict security requirements around the world."
The company said there was only one Blackberry enterprise solution available around the world and it remains unchanged in all markets.
RIM cooperates with all governments with a consistent standard and the same degree of respect, the company said.
"Any claims that we provide, or have ever provided, something unique to the government of one country that we have not offered to the governments of all countries, are unfounded," RIM said.