The figure was the lowest since the second quarter of 2012. Since then, Samsung's operating profit hasn't fallen below $7 billion, largely driven by robust sales of Galaxy smartphones.
Samsung, which usually doesn't elaborate on its financial performance until its full report later in the month, issued a rare statement to explain its result, which Nomura analyst Chung Chang-won described as "very disappointing."
The company blamed the lower profit on the South Korean currency's appreciation against the U.S. dollar and the euro, as well as most emerging market currencies. The won hit a 6-year high against the U.S. dollar earlier this month.
It also said sales of medium- and low-end smartphones were weak in China and in some European countries because of stronger competition and sluggish demand. Fewer consumers in China bought handsets that run on 3G mobile networks as they waited for faster 4G networks.
Samsung, which earlier this year vowed to aggressively expand its tablet sales, acknowledged it faced some challenges in selling tablet computers. Consumers weren't replacing their tablet PCs as often as smartphones, while smartphones with a giant screen of 5 or 6 inches, such as Samsung's Galaxy Note series, replaced demand for smaller tablets that measure about 7 or 8 inches.
"Expectations have been lowered on Samsung," said Will Cho, an analyst at KDB Daewoo Securities. "With intensified competition in the mid- and low-end smartphones, it will be tough to stay as lucrative as in the past."
About three in every 10 smartphones sold globally were made by Samsung in 2013 and the company's handset sales will likely improve during the current quarter. But Cho said how much profit it can take would be more important than how many handsets it can sell because most sales growth would come from cheap smartphones.
In the cheap smartphone market, Samsung faces an uphill battle against brands such as Xiaomi and Lenovo.
Xiaomi, an upstart Chinese company that is moving into other Asian countries, surprised the industry with its $100-level smartphones that were snapped up by fans. Counterpoint Technology Market Research said last month that Xiaomi's $130 smartphone Redmi was the most-sold mobile device in China in April, beating Apple's iPhone and Samsung's Galaxy.
Samsung shifted its focus to affordable smartphones, tablets and wearable devices, such as the Gear smartwatches, to offset falling profit but they are yet to arrest the declining earnings from smartphones and components in mobile devices that Samsung supplies such as memory chips and display screens.
Shares of Samsung closed 0.2 percent higher in Seoul as the company gave an outlook that appeared to reassure investors.
"The company cautiously expects a more positive outlook in the third quarter with the coming release of its new smartphone lineup," it said. "Samsung expects stronger smartphone sales and this will have a positive impact on the company's display panel businesses."
But some analysts were not convinced about Samsung's long-term prospects.
"Though we anticipate some positive earnings impact for the component businesses (in the third quarter), we see growing uncertainty over Samsung's future earnings in the long-term," Chung, the Nomura Financial Investment analyst, said in a commentary.
Chung cited Apple's upcoming release of the iPhone 6, the increasing difficulty in standing out from a plethora of other Android devices and the falling appeal of premium smartphones, a reminder of the PC market that came to be flooded with cheap almost identical products.
Samsung is expected to announce an upgrade of the Galaxy Note series in the fall around the time when Apple usually upgrades its iPhone.