North Korea on Sunday launched 25 tactical missiles into the sea in a likely protest of ongoing U.S.-South Korea military drills, the Yonhap News Agency reported.
The projectiles flew approximately 43 miles before splashing down in international waters, the South said.
The South Korean military said it was observing a state of top combat preparedness in the event of future missile launches. "[We] call on North Korea to stop further provocative actions," the South Korean Joint Chiefs of Staff said.
Though Pyongyang is prohibited by the U.N. Security Council from using ballistic-missile technology, it is not barred from the short-range missile and rocket test-firings of the sort conducted on Sunday, according to Reuters.
"We once again call on North Korea to refrain from provocative actions that aggravate tensions," U.S. State Department spokeswoman Jen Psaki said in released comments.
North Korea in recent weeks conducted a number of ballistic-missile firings, including one that endangered a Chinese passenger plane that was flying nearby. Those launches were seen also as retaliation against the U.S.-South Korea armed forces exercises.
Chinese Foreign Ministry spokesman Hong Lei on Monday urged all sides to remain calm, Yonhap separately reported.
"We hope that all relevant parties will do more that is conducive to peace and stability of the Korean Peninsula and relax tensions at the moment," Hong told reporters.
"Additional measures will be taken to demonstrate its might one after another as long as the U.S. nuclear threat and blackmail persists," the commission said in a statement disseminated by official media.
South Korea-based experts said the statement could mean Pyongyang was considering several provocative actions: announcing new headway in its uranium enrichment program, another test-launch of a long-range missile, or a fourth nuclear explosion.
"This warning is not about an imminent action but an expression of frustration with Washington, which refuses to budge an inch despite Beijing's efforts to draw it back to dialogue" with the North, Professor Yang Moo-jin said in an interview.