The six are Mozambique, Tanzania, Timor Leste, Burundi, Haiti, and Cambodia.
Prime Minister Nguyen Xuan Phuc said the Ministry of Defense -- which owns the company -- would take responsibility for the task.
The other four countries it operates in are Laos, Peru, Cameroon, and Myanmar.
In a global ranking released last month by Brand Finance, a British brand valuation consultancy, Viettel, Vietnam’s largest telecommunication service provider, jumped nine places to 28th with its brand valued at $5.8 billion, up 34.4 percent from a year earlier.