On Friday, North Korea appealed to the people, organizations and political parties of South Korea to join them in their “anti-war” effort against the US.

In a letter of plea, the Central Committee of the Korean Social Democratic Party wrote, "All the parties and people from all walks of life in South Korea should rise up in the anti-US, anti-war struggle for peace, clearly seeing through the nature of the US, the chieftain of aggression and disturber of peace."

The already strained relationship between the northern and southern parts of the Korean peninsula has grown more tense lately as Seoul engages in its annual joint military exercises with the US, which has prompted many threats from Pyongyang and its supreme leader, Kim Jong-un.

Pyongyang isn’t alone in its aggressive posturing, however. US President Donald Trump has accused the communist nation of "acting very badly," as his Secretary of State Rex Tillerson heavily implied that Washington is willing to take military action against provocation from North Korea, signaling the end of what he called the “strategic patience” used by former President Barack Obama.

Published by the state-sponsored Korean Central News Agency, the letter characterized the computer-based Key Resolve and ground-based Foal Eagle drills as "rehearsals for a nuclear war," stating that "All Koreans should turn out in the struggle to resolutely check the reckless nuclear war drills of the US and South Korean warmongers," according to South Korea’s Yonhap News Agency.

North Korea fumed at the fleet of aircraft carriers led to the peninsula by the USS Carl Vinson, threatening "merciless" strikes if Pyongyang’s sovereignty was violated, and said the North would reduce the US "to ashes" if they conducted a preemptive strike.

This letter comes as the South Korean military warns of an imminent nuclear test from the North, possibly in the first week of April. It is thought that the supposed test, which would be the country’s sixth, could take place as Trump meets with Chinese President Xi Jinping at the US president’s Mar-a-Lago resort in Palm Beach Florida.

On Thursday, Trump predicted that his meeting with Xi would be "a very difficult one," writing on Twitter that job losses and trade deficits, which he blames on an unbalanced relationship with the Asian power, could no longer be tolerated.