Evan Vucci/AP US President Donald Trump speaks as Secretary of State Mike Pompeo looks on during a news conference after the summit with North Korean leader Kim Jong Un in Hanoi, Vietnam, on Thursday, February 28. In pictures: Trump-Kim summit in Vietnam cut short

Evan Vucci/AP US President Donald Trump speaks as Secretary of State Mike Pompeo looks on during a news conference after the summit with North Korean leader Kim Jong Un in Hanoi, Vietnam, on Thursday, February 28.

The second summit between US President Donald Trump and North Korean leader Kim Jong Un ended abruptly on Thursday, with a working lunch and a scheduled signing ceremony being called off.

The two leaders, meeting in Hanoi, Vietnam, were unable to reach a joint agreement as they did in their first summit last year.

Trump told reporters afterward that the talks were "very productive," but he said he decided there was no agreement worth signing. "Sometimes you have to walk, and this was just one of those times," said Trump, who added that the summit ended on friendly terms.

This was just the second time ever that a sitting US president had met with a North Korean leader. The first came in June, months after the two leaders traded insults and threatened each other with nuclear annihilation. That summit ended with a joint agreement to "work toward complete denuclearization of the Korean Peninsula," and Trump said he'd developed a "special bond" with Kim.