It would mark their first trilateral summit, as well as an unprecedented visit by a North Korean leader to the U.S.
Speaking to reporters during his visit to Britain, Kang said: "We cannot rule out (the possible trilateral summit)," according to comments carried by local news agency Yonhap on Thursday.
The North's Chairman Kim Jong-un apparently accepted an invitation by Trump to visit the U.S. when the pair held a groundbreaking denuclearization meeting in Singapore last month.
But critics have questioned Pyongyang's commitment to giving up its nukes given the lack of progress since the Trump-Kim summit on June 12.
Kang insisted the goal of North Korea's complete denuclearization is "unflappable," even if it takes time -- echoing the recent admission by Trump that there is "no time limit" for the North.
She added that diplomatic efforts will be made towards another major ambition on the peninsula -- declaring a formal end to the 1950-53 Korean War within this year, as agreed during April's inter-Korean summit.
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