James Martin/CNET

The digital divide is showing signs of closing, the National Telecommunications and Information Administration said Wednesday.

More than 13 million users -- including low-income families, seniors, African Americans and Hispanics -- have signed on to the internet over the past two years, according to the agency, part of the US Department of Commerce. Much of that access occured on mobile devices. For the first time, more people are accessing the web on tablets than on desktops, the NTIA said. Sales of desktop computers have been on a steady decline for the past few years.

The report illustrates the importance of internet access on mobile devices. "The digital divide is showing signs of giving way as more Americans from all walks of life connect to the Internet," the NTIA said in its report. "Several historically disadvantaged groups showed significant increases in online adoption."

According to the report, 63 percent of US seniors now access the internet. That's a 7 percent increase from 2015. Usage among low-income households grew to 62 percent, compared with 57 percent two years ago.

Tablet usage among Americans grew to 32 percent from 29 percent in 2015. Desktop computer use slid to 30 percent from 34 percent.

Smartphone usage continues to rule internet usage, with 64 percent of Americans using the devices regularly.