Japanese Prime Minister Shinzo Abe has demanded the release of two Japanese hostages that appeared in an Islamic State (Isis) video, describing the threat to kill them as "unforgivable".

Abe condemned what he said were acts of terrorism in a press conference. "It is unforgivable and I feel strong resentment," he said of the video's content.

"Their lives are the top priority," Abe said. "Extremism and Islam are completely different things."

The two men, believed to be Kenji Goto Jogo and Haruna Yukawa, are seen in orange jumpsuits either side of a militant dressed in all black in the footage released by Isis.

The militant, believed to be "Jihadi John", who is also seen in the execution videos of western hostages James Foley, Steven Sotloff, David Haines and Alan Henning, demands Japan pay $200m (£132m, €173m) within 72 hours to secure the hostages' release.

Abe, who is in Jerusalem as part an official six-day tour of the Middle East, said the government was in talks with its Israeli counterpart to gather information on the captives.

The prime minister has cancelled all of his other engagements apart from his meeting with Palestinian Authority President Mahmoud Abbas, according to his chief government spokesman.