The statement came a day after the allies launched their combined military drill as scheduled, despite the North's strong complaint against the maneuvers with a series of missile launches.

The North has long condemned the exercise as a rehearsal for invasion.

Calling the exercise a "violation" of a series of agreements Seoul and Washington signed with Pyongyang, the statement said the North will make them "pay heavy price" if they ignore its repeated warnings.

"The US and South Korean authorities remain outwardly talkative about dialogue. But when they sit back, they sharpen a sword to do us harm," it said. "If this is what they call 'creative approach' and 'imaginative power beyond common sense,' we will be compelled to seek a new road as we have already indicated."

Also slamming Seoul and Washington over the introduction of weapons, such as stealth fighters, to South Korea, it said such a move shows that the two "do not have political will at all to implement the joint statements," where they committed to improving the US-North Korea and inter-Korean relations.

"We remain unchanged in our stand to resolve the issues through dialogue. But the dynamics of dialogue will be more invisible as long as the hostile military moves continue," it said.

On Friday, North Korea fired two short-range projectiles into the East Sea, just two days after it launched two short-range ballistic missiles, according to the JCS. On July 25, Pyongyang also fired two rounds of a new type of ballistic missile, resuming its weapons testing after 77 days.

An official of South Korea's unification ministry said the North appears to be trying to boost its bargaining power ahead of the resumption of its denuclearization negotiations with the US.

Their working-level talks had been expected to resume in mid-July, but they have not taken place yet.

"North Korea's recent series of military moves are seen as an attempt to boost internal unity while securing an upper hand in the upcoming political situation and boosting its bargaining power," the official said.

Despite the launches, US seemed to remain upbeat about the prospects for talks with the North until last week, with US President Donald Trump saying Friday that the tests do not violate any agreement between him and North Korean leader Kim Jong-un.

"South and North Korea as well as the US are all trying to keep the situation under control," the official said. (Yonhap)