Just days after a failed missile launch, North Korea has fired apparent artillery into the sea on Sunday, according to South Korea’s Defense Ministry. It is unclear what munitions were fired, but global experts warn that the ramp-up in testing could pave the way for the rogue nation to launch its longest-range ballistic missile, in an attempt to put pressure on the U.S. to come back to the negotiation table. On Wednesday, North Korea’s Hwasong-17 missile is thought to have misfired, exploding in midair.