SEOUL - North and South Korea are discussing a possible non-aggression pledge by the United States to the North and a start of peace treaty talks to address Pyongyang's security concerns before a North Korea-US summit, a senior South Korean official said on Sunday. South Korean President Moon Jae-in and North Korean leader Kim Jong Un held a surprise second meeting on Saturday after U.S. President Donald Trump called off his talks, set for June 12 in Singapore, before floating a reinstatement of the plan. 'For the success of the North Korea-US summit, we're exploring various ways of clearing North Korea's security concerns at the working level,' the senior South Korean presidential official told reporters. 'That includes an end to hostile relations, mutual non-aggression pledge, a launch of peace treaty talks to replace the current armistice,' the official said. The two Koreas are also in talks over a three-way declaration of the end to 1950-53 Korean War but there has not been any agreement yet over a tripartite summit, the official said.