Yonhap News Agency screen grab of China's leader Xi Jinping (L) and North Korea's Kim Jong Un.

North Korea and China are having second thoughts about being communist brothers.

Korea JoongAng Daily reported that cracks in the alliance between the two nations widened on Thursday as Pyongyang labeled Beijing a traitor, while China expressed skepticism about renewing a 56-year-old friendship and mutual assistance treaty.

The North’s Korean Central News Agency issued a rare attack saying that China had crossed a “red line” in their relationship, characterizing recent Chinese moves as a “disloyal and betraying act.” The statement was the North’s response to China’s intensifying pressure over its nuclear arms program.