"We're concerned about these repeated violations of Security Council resolutions that create, I think, greater prospects for instability and insecurity," Blinken told reporters after US-EU trade talks in Pittsburgh.

North Korean leader Kim Jong Un earlier Thursday was quoted in state media as condemning a US offer of dialogue, calling it a "petty trick."

Blinken said the United States could not confirm North Korea's claim to have tested a hypersonic gliding missile, a potential game-changer as it can fly five times the speed of sound.

"We're evaluating and assessing the launches," Blinken said, "to understand exactly what they did, what technology they used, but regardless, we've seen repeated violations now of UN Security Council resolutions that the international community needs to take very seriously."

The United States, Britain and France have called a Security Council meeting on North Korea that is set to take place Friday.

Blinken also vowed full support for any measures to ease tensions by South Korea, part of President Joe Biden's emphasis on working with allies.

"Certainly, if there are any measures that can appropriately reduce the risks that exist, that probably makes sense," Blinken said of South Korean efforts.