Domestic subscriptions were even lower - less than a million Americans signed up for the service during the past three months - and the numbers fell 37 per cent short of Pivotal Research Group's estimate of 1.2 million.
Moving forward, Netflix forecasts a total revenue of US$3,988 million for Q3 18.
Netflix shares plunged in after-hours trading in NY after the company's latest results signalled it was facing stronger competition for customers.
In its trying-hard-to-be-positive letter (PDF) to shareholders, Netflix said that it had "a strong but not stellar Q2, ending with 130 million memberships".
But Netflix missed its target badly in the April-June period, causing its high-flying stock to plummet by about 14pc to $345.63 (€294.63) in extended trading.
On Wall Street, the slowdown is raising questions about whether Netflix can sustain the rapid-fire growth that has made it one of the hottest companies in tech, especially as bigger players crowd its turf.
Netflix said operating margins would be narrower than previously expected because of the rapid strengthening of the USA dollar, which appreciated by more than 5 percent against major trading partners' currencies in the second quarter.
During the second quarter, global net adds totaled 5.15 million.
That comes out to 4.87 million new subscribers for the quarter, far below the 6.2 million Netflix was hoping for.
Netflix said it added just 670,000 subscribers in the US for the period ending in June, about half of its own projection of 1.2 million. Earnings grew 32 percent from previous year to $384 million, or 85 cents per share. The company debuted its first Danish and first Indian dramas in the quarter, and it plans to release a new foreign-language program at least once a week next year.
The company blamed the strengthening of the USA dollar for the lack of worldwide growth, and it acknowledged there is more competition from HBO and Walt Disney Co.
Hastings said the company would make adjustments to account for foreign exchange rates in order to "steadily" increase operating margins.
But it also faces growing competition. And AT&T Inc has promised to boost investment in HBO after taking over the network in its Time Warner acquisition.
At the same time, cable distributors are offering smaller and cheaper bundles of channels. "Our strategy is to simply keep improving, as we've been doing every year", the company said.