Construction of a $70-million undersea cable promising nationwide high-speed internet will be completed next week, three years after the project was debuted, it was announced on Thursday.

The 1,300 km Malaysia-Cambodia-Thailand cable will officially be connected on Monday, Kith Meng, chairman of the Cambodian-owned conglomerate Royal Group, told Prime Minister Hun Sen and government ministers on Thursday.

He announced the date in response to a question from Mr. Hun Sen during the inauguration of a newly completed $7.69 million Ministry of Post and Telecommunications building on Monivong Boulevard in Phnom Penh.

An agreement to build the connection—which will be linked to a 20,000 km underwater cable that connects Asia to the U.S.—was formalized in May last year by internet provider Ezecom, a subsidiary of Royal Group; Thailand’s Symphony Communication; and Malaysia’s Telekom Malaysia. The project has been hampered by repeated delays.

Smartphones and social media users have driven major growth in the number of Cambodians accessing the internet, with 7.7 million people now connected to the web compared to 2.7 million in 2012, Telecommunications Minister Tram Iv Tek said, adding that 19.3 million mobile phone SIM cards were in use as of September.

The rapid uptick in mobile devices and high demand for information-sharing technology showed the need for faster internet speeds and expansion of networks to rural areas, Mr. Hun Sen said.

“Even ox-cart drivers are using phones. Although some could not afford smartphones, at least they could use the cheaper one with the flashlight,” he said.

“Today, the use of advanced information technology is more effective,” he said. “Even I still do more research myself.”

New government employees and officials seeking promotions are required to possess knowledge of modern technology, Mr. Hun Sen said, including how to use smartphones and encrypted messaging applications like WhatsApp and Telegram, which he frequently uses to communicate with other parliamentarians.

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