Kim Jong Un and other top officials in North Korea are able to keep their phone conversations private by using one of two private cellular networks inside the country, a telecommunications engineer who once worked for the government said Thursday. One network is for ordinary citizens, while the other is for Pyongyang's government elite, the engineer said.

The civilian network, known as Koryolink, was built with help from an Egyptian cell phone company in 2009, the engineer said.

The network for officials was built without foreign help, he said. "They have another network for the VIPs that is totally separated from everything … a 3G network that is not accessible to normal users," said engineer Ahmed El-Noamany, who worked in North Korea between 2011 and 2013. "This is a special network which has its own things -- own algorithms, own operating system, own everything."

Western sanctions against Pyongyang had prevented the country from obtaining vital encryption technology, El-Noamany said, reported NK News, a U.S. website that covers news from the Korean Peninsula. In most modernized countries, encryption technology prevents unauthorized people from listening to phone calls. However, such technology doesn’t exist in North Korea, so that made building private networks the best available option.

“They cannot provide such sophisticated technology at their end because, again, sanctions are keeping them like 40 years back,” El-Noamany said. “So in order to overcome this sophisticated technology issue, they came up with a very nice solution: Let’s have our own network."

The acknowledgment of the networks adds another layer of intrigue to the famously secretive state. To maintain that secrecy, current cell phone networks do not allow citizens to make international calls, NK News reported. Likewise, international embassies are unable to make domestic calls to civilians. Tourists can also get subscriber identification module (SIM) cards, but are able to call only fellow tourists.

Those controls are part of Pyongyang’s strict policy on preventing information from coming in or going out of the country. The civilian network has attracted more than 2.5 million users.

Koryolink is a joint venture between the North Korean government and Egypt's Orascom Telecom and Media Technology.