Netflix shares fell sharply after the video streaming firm added fewer subscribers than expected ahead of US prices rises.

The company added 1.68 million users in the three months to June - well below its forecasts of 2.5 million.

Subscriber cancellations rose "slightly and unexpectedly" ahead of higher charges for existing users.

The numbers sent Netflix shares down 13% to $85.90 in after-hours trading in New York.

If that loss extends when Wall Street opens on Tuesday, the stock will have lost about a quarter of its value this year.

Netflix shares are often subject to big swings as investors bet on its drive to redefine global television viewing habits.

Wedbush Securities analyst Michael Pachter said: "The shares are down because their domestic subscriber growth slowed to a crawl ... and domestic profits fuel their international losses."

Netflix admitted that growth had slowed both in the US and international markets: "We are growing, but not as fast as we would like or have been."

Analysts estimate that about 20 million subscribers may be forced to pay between $1 and $2 more a month by the end of this year.