Abe and other Japanese officials declined to discuss whether they'd pay the ransom for captives Kenji Goto and Haruna Yukawa, though their armed forces generally only operate in a self-defense capacity at home.
Their kidnapping also immediately recalled the 2004 beheading of a Japanese backpacker in Iraq, carried out by the Islamic State group's predecessor over Japan's involvement in the US led war there.
Japanese officials said they would analyze the tape to verify its authenticity, though Abe offered no hesitation as he pledged to free the men while speaking to journalists in Jerusalem.
"It is unforgivable," said Abe as he wrapped up a six-day visit to the Middle East. He added: "Extremism and Islam are completely different things."
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In the video, the two men appear in orange jumpsuits with a rocky hill in the background, a masked militant dressed in black standing between them. The scene resembles others featuring the five hostages previously beheaded by the Islamic State group, which controls a third of Iraq and Syria.
"You have proudly donated $100 million to kill our women and children, to destroy the homes of the Muslims ... And in an attempt to stop the expansion of the Islamic State, you have also donated another USD 100 million to train the (apostates)."
The militant's comments likely refer to money Abe pledged while in Egypt to help Iraq's government and aid Syrian refugees.
The premier also said the Israeli government, which Japan promised Sunday to cooperate with on counterterrorism, are sharing information to aid in the hostage crisis. The Israeli prime minister's office declined to comment.