North Korea test-fired two medium-range ballistic missiles on Wednesday, South Korea and the US said, a defiant challenge to a rare three-way summit of its rivals Seoul, Tokyo and Washington that focused on the North's security threat.The missiles flew about 650 kilometers (400 miles) off North Korea's east coast early Wednesday morning, South Korean Defense Ministry front man Kim Min-seok said. It wasn't immediately clear where the missiles splashed down. Kim said the missiles were likely fired from a mobile launcher.