Former U.S. Vice President Joe Biden, who is the Democratic Party's presidential candidate, says he is open to meeting with North Korean leader Kim Jong-un, if Kim agrees to move forward in denuclearization.

During a presidential debate broadcast live on Thursday in the U.S., Biden said the condition to a possible summit meeting would be Kim's agreement to reduce the North's nuclear capacity for a nuclear-free Korean Peninsula.

Biden also referred to Kim as a "thug," when accusing President Donald Trump of legitimizing Pyongyang and its dictator.

Trump, for his part, reiterated that he has a "very good relationship" with Kim, claiming his friendship with the North Korean leader has helped avoid war.