DHAKA, April 26 (Xinhua) -- Bangladesh's second largest mobile phone operator Robi Axiata Limited has celebrated the milestone of 1 million 4G customers it achieved with its advanced 4.5G technology.

In the fourth-generation arena, Robi, a joint venture of Axiata Group Berhad (Malaysia), Bharti Airtel Limited (India) and NTT DoCoMo Inc. (Japan), in the celebration ceremony on Thursday said that it is the first mobile phone operator to reach this milestone in the country.

Since the launching of the 4.5G service in February, Robi said it has so far expanded its 4.5G network in all the 64 districts of the country with more than 4,700 4.5G sites.

The network expansion took place following the launch of the 4G service on Feb. 20 this year, said the operator in a statement.

Robi's managing director and CEO Mahtab Uddin Ahmed said the company has invested around 30 billion taka (355 million U.S. dollars) so far for 4G service and the investment will continue in the future.

According to Bangladesh Telecommunication Regulatory Commission (BTRC) data, the number of mobile subscribers in the country reached 148.769 million in February with addition of 3.66 million new users in the first two months of the year.

Bangladesh has now four mobile companies, three of whom including Grameenphone, Robi and Banglalink are foreign-backed cellphone operators.

The number of subscribers of the mobile operators, Grameenphone, Robi Axiata, Banglalink and Teletalk stood at 66.466 million, 45.595 million, 32.720 million and 3.988 million respectively at the end of February, BTRC data showed.

The total number of Bangladesh's mobile phone subscribers reached nearly 145.114 million at the end of December 2017.