North Korea fired suspected artillery pieces into the sea on Sunday, South Korea’s military said, days after the North’s latest missile launch ended in failure amid the country’s recent burst of weapons testing activity.

There is speculation that North Korea could soon try to launch its developmental longest-range ballistic missile to bolster its weapons arsenal and dial up pressure on the United States to wrest concessions amid stalled diplomacy. South Korea’s military suggested North Korea’s mid-air missile explosion last Wednesday involved parts of its Hwasong-17 missile, its biggest weapon.

On Sunday, South Korea’s Defence Ministry said it detected firings likely