US President Donald Trump has said U.S.-led international sanctions were the sticking point that caused his summit meeting with North Korea's Kim Jong Un to break up without agreement early Thursday.

Trump was speaking in Hanoi, Vietnam, after he announced that he had walked away from the summit without a deal being reached.

He explained the abrupt end to the summit by telling reporters: "Sometimes you have to walk."

Trump said Thursday that Kim wanted him to lift US sanctions on the country in exchange for denuclearization, but he wasn't willing to do that.

He says the American side asked Kim to do more "but they weren't willing to do an area that we wanted."

Trump and Kim departed the hotel where they've been holding summit negotiations far earlier than planned Thursday.

A joint agreement signing ceremony was scrapped.