North Korea fired two short-range ballistic missiles into the East Sea in the latest saber-rattling move amid the ongoing South Korea-U.S. military drills, South Korea’s military said Thursday.

According to the Joint Chief of Staff (JCS), the two missiles were fired around 5:20 a.m. from North Hwanghae Province and hit waters northeast of the port city of Wonsan off the country’s east coast.

Sources said the pair flew some 500 kilometers.

“The military is keeping close tabs on the situation and is prepared to deal with any North Korean provocations,” the JCS said.

The latest provocation followed the North’s test-firing a week ago of a new 300-millimeter-caliber multiple launch rocket system.

Pyongyang has been ratcheting up its bellicose threats against Seoul and Washington as the allies are staging the Key Resolve and Foal Eagle exercises, a command post exercise and field training war game, respectively. The weekslong exercises began Monday.

A day earlier, the North threatened to turn the allies’ military installations into a “sea of fire” in a commentary published by its official Korean Central News Agency. The North has accused the allies of conducting the drills to “decapitate” its leadership and prepare for a “nuclear war of invasion.”

Observers say Pyongyang’s continued provocations also reflect its anger at the recent adoption of a U.N. Security Council sanctions resolution that punishes the isolated regime for its Jan. 6 nuclear test and Feb. 7 long-range rocket test.