Businesses around the world are set to spend more on Internet advertising than on television commercials for the first time in 2017, forecaster ZenithOptimedia said on Monday.

Zenith said it expects Internet advertising to grow at more than three times the rest of the industry in 2016, driven by demand for ads on social media, online video and paid search.

The forecaster said in December it expected ad spending on the internet to overtake TV only in 2018.

"The global economy faces clear challenges," it said. "But advertisers' confidence has remained largely unshaken, and our forecasts for global growth in 2016 have barely changed since we published our last forecasts in December."

ZenithOptimedia, owned by France's Publicis, trimmed its expectation for growth in global advertising this year to 4.6 percent from a forecast of 4.7 percent it gave in December. That is still ahead of 3.9 percent growth in 2015.

The industry will be boosted in 2016 by advertising around the Rio Olympics, the European soccer championships and the U.S. Presidential election.

However, conditions in China, Russia and Brazil, along with uncertainty regarding Britain's membership of the European Union, were among the challenges to the global economy, it said.