• North Korea could soon boost the ante, according to US and South Korean sources.
• The sources claim Kim Jong Un is almost ready to detonate another nuclear device at his country’s nuclear test site.
• The South Korean and US forces flew 20 fighter planes over the waters off South Korea’s western coast in a show of force.

Read More: The US and South Korea have launched missiles into the sea

The United States and South Korea fly

Read More: U.S, S. Korea launch ballistic missiles in response to North Korea launches

A senior US official warned of a harsh response if North Korea conducts its first nuclear test in nearly five years.

The Joint Chiefs of Staff of South Korea said the air show featured 16 South Korean planes, including F-35A stealth fighters, and four American F-16 fighter jets; and was intended to demonstrate their capacity to respond quickly to North Korean provocations.

The flight came a day after the allies fired eight surface-to-surface missiles into South Korea’s eastern waters to equal North Korea’s weekend missile display, which blasted the same number of weapons from several places in what was likely the country’s largest single-day testing operation.