Japanese Prime Minister Shinzo Abe vowed to avenge the deaths of two countrymen killed by extremist Muslim organisation the Islamic State (IS) after a new beheading video was released over the weekend.

The terrorists executed journalist Kenji Goto in a video published Saturday—a week after IS published a death photo of aspiring military contractor and Japanese citizen Haruna Yukawa.

Abe promised "to make the terrorists pay the price," and condemned the actions of the militants in a statement. 

"I am infuriated by these inhumane and despicable acts of terrorism, and resolutely condemn these impermissible and outrageous acts," he said.

"I will never forgive these terrorists. I will work with the international community to hold them responsible for their deplorable acts."

Yukawa, 42, was first captured in Syria in April 2014, but released with the help of Goto, 47. Yukawa reentered Syria months later, and was captured a second time in July 2014. Goto entered Syria in October, reportedly to rescue Yukawa. Abe said he grieved for their families. 

"I am rendered simply speechless," he intimated. "When I think about the unbearable pain and sorrow that his family must be feeling, I am rendered simply speechless.

"As a government, we have pursued every possible means to save their lives. We feel greatest sorrow and profound grief."

IS demanded $200 million for the release of Goto and Yukawa after Abe pledged the same amount in non-military aid to countries fighting the terrorists in Iraq and Syria. A former Japanese diplomat and foreign affairs advisor to Abe called the executions a wake-up call. 

"This is 9/11 for Japan," Kunihiko Miyake insisted. "It is time for Japan to stop daydreaming that its good will and noble intentions would be enough to shield it from the dangerous world out there.

"Americans have faced this harsh reality, the French have faced it, and now we are, too." 

While Japan remains a pacifist country, Abe will reportedly seek to expand the role of the military legislatively in the coming weeks.

"No country is completely safe from terrorism," he told Parliament last week. "How do we cut the influence of ISIL, and put a stop to extremism? Japan must play its part in achieving this."