AT&T will invest approximately $3 billion in Mexico to make its high-speed mobile internet network available to 100 million people by the end of 2018.

The US giant has already spent $4.4 billion in the country this year after acquiring Mexican mobile unit Iusacell for $2.5 billion and Nextel Mexico for $1.9 billion, in a bid to fuel competition with America Movil and Spain’s Telefonica.

AT&T said the first phase of the investment will be complete in the next six months, to cover 40 million people, equating to one third of the population.

The network will reach 75 million by the end of 2016 and be completed by year end 2018.

As part of its strategy, the company plans to leverage its US network, and expand it to create a “North American Mobile Service”, covering 400 million people and businesses across Mexico and the US.

This will enable Mexican customers to use their individual mobile plans for voice and data while in the US. Customers on these plans can also use their voice minutes to call people in the US, who are on an AT&T network.

Chief executive Randall Stephenson outlined the investment during talks with Mexican president Enrique Pena Nieto on Thursday.

“We are building a network in Mexico that is capable of bringing innovation and economic vitality to the country, just as we have done the US,” Stephenson said in a statement. “This seamless network will link together our two countries’ economies, peoples and cultures like never before.”

Stephenson said the telecoms reforms in the country, introduced by Nieto and regulator Ifetel, had given AT&T “the ability to invest in building an advanced mobile network in Mexico”.

The government introduced a range of reforms in 2013, which are designed to limit the dominance of market leader America Movil and give more opportunities to foreign investors and smaller players.

AT&T said Iusacell had six million subscribers at the end of March, while Nextel Mexico had approximately three million subscribers when it was acquired in April.