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Google parent Alphabet's latest profit figures have missed forecasts, sending the tech giant's shares falling in extended trading on Wall Street.

Profits rose 8% to $5.3bn (£4.2bn) for the last three months of 2016, fuelled by more advertising on mobile phones and YouTube.

But analysts had expected more, and Alphabet's shares fell almost 3% .

However, revenue for the quarter topped $26bn, up 22% from the same period the year before.

Google's advertising revenue, which accounts for the bulk of its business, rose 17.4% to $22.40bn in the quarter.

Paid clicks, or clicks on Google ads, rose 36%, compared with a 33% increase in the third quarter. Paid clicks are those ads on which an advertiser pays only if a user clicks on them.

"Our growth in the fourth quarter was exceptional," Alphabet chief financial officer Ruth Porat said in a statement. "We're seeing great momentum in Google's newer investment areas and ongoing strong progress in Other Bets."

'Tremendous potential'

For earnings purposes, Alphabet separates operations such as self-driving cars and broadband into its Other Bets category, which nearly doubled revenue to $262m in the quarter but still posted a loss of nearly $1.1bn.

Under its new structure, Alphabet is seeking to expand beyond its role as a search engine and develop new revenues streams.

Ms Porat pointed to growth app sales, hardware and the cloud business. "We see tremendous potential ahead for these businesses, as well as in the continued development of non-advertising revenue streams for YouTube," she said.