WASHINGTON —The United States on Saturday sternly admonished North Korea against acts that could "further destabilize" the region, amid claims that it successfully tested a new engine designed for an inter-continental ballistic missile that could reach US shores.

"We have seen the reports of North Korea's claims to have developed new engine technology for its ICBMs," read a statement from State Department Deputy Spokesman Mark Toner.

"We call on North Korea to refrain from actions and rhetoric that further destabilize the region and focus instead on taking concrete steps toward fulfilling its commitments and international obligations," Toner said.

North Korea said its breakthrough would "guarantee" an eventual nuclear strike on the US mainland.

It was the latest in a series of claims by Pyongyang of significant new inroads in both its nuclear weapons and ballistic missile programs, although outside experts have treated a number of the claims with skepticism.

According to the North's official KCNA news agency, the ground engine test was ordered and personally monitored by the hermit nation's enigmatic leader Kim Jong-Un.