The two projectiles, fired on Tuesday morning local time, were assessed to be similar to the short-range ballistic missiles tested by North Korea last week, the official said.
The South Korean Joint Chiefs told Yonhap news agency that the projectiles were fired from areas near the South Hwanghae Province.
"We continue to monitor the situation and are consulting closely with our South Korean and Japanese allies," a senior U.S. administration official told ABC News in a statement.
The latest test comes as U.S. Defense Secretary Mark Esper is in the region for meetings this week with his Japanese and South Korean counterparts and the U.S. and South Korea began joint military exercises on the Korean peninsula.
A spokesperson for North Korea's Foreign Ministry decried the exercises, which are computer-based and have been scaled down in size from previous years, as "an undisguised and a flagrant violation" of agreements between the U.S. and North Korea.
"Although the U.S. and South Korean authorities are playing all sorts of tricks to justify the joint military exercise, its aggressive nature can neither be covered up nor whitewashed in any manner," the spokesperson said on Tuesday.
Last Thursday, North Korea launched at least one short-range ballistic missile into the Sea of Japan, assessed to be similar to the missiles tested earlier that week.
President Donald Trump downplayed that launch, saying, "Short-range missiles, we never made an agreement on that. I have no problem. We'll see what happens. But these are short-range missiles. They are very standard."