Social networking site Facebook is to launch advertising clips on users' news feeds this week, the Wall Street Journal website reported on Tuesday.

The newspaper, quoting an anonymous source close to the matter, said that the clips would be triggered automatically on feeds when a user consulted his or her profile either on the Internet or via a smartphone.

Facebook was expected to announce the development on Tuesday and the advertisements would be launched on Thursday, beginning with an ad for the science-fiction film "Divergent" to be released in the first half of next year.

The launch of advertising clips has been delayed several times in recent months, first because of concerns that this might drive customers away and also because of technical problems, the newspaper said.

The clips could last for up to 15 seconds, and an advertiser wanting to reach all Facebook users aged between 18 and 54 might have to pay $2.0 million (1.45 million euros) per day.

The company, which like all free sites, draws most of its income from advertising, raised its income from this source in the third quarter of the year. Advertising revenue showed a 66-percent rise over 12 months to $1.8 billion.

The share of advertising income from connections by mobile devices to the network, watched closely by investors, rose further and now accounts for 49 percent of the total from 41 percent in the second quarter.

The report said that the ads "may help Facebook capture a share of the $66.4 billion advertisers are expected to spend on US television this year."