Relatives of Japanese nationals abducted by North Korean agents expressed disappointment Thursday with the apparent lack of progress on the decades-old issue during a summit between U.S. President Donald Trump and the North's leader, Kim Jong Un.

Following a telephone conversation with Trump when he was briefed on the leaders' Hanoi summit Prime Minister Shinzo Abe told reporters that the U.S. president had raised the issue with Kim, but the matter did not come up at a post-summit news conference.

The abductions, which were carried out during the 1970s and 1980s, remain one of Japan's biggest grievances against North Korea and have been a major hurdle to establishing formal diplomatic ties.