For days now, a crowd has gathered outside the Japanese prime minister's house in Tokyo to call for the release of Kenji Goto, a Japanese journalist being held by the Islamic State in Syria.

On Sunday, after a video purportedly showing Goto's beheading was released online, the crowd gathered once again, this time for a vigil mourning the loss of the slain journalist.

Mourners held placards saying: "Kenji, you will be alive in our memories" and "no war."

Others held up photos of Goto and fellow Japanese citizen Haruna Yukawa, who was killed by militants last week.

Separately, Goto's mother, Junko Ishido, read a statement to reporters. "Kenji has left for good. I am lost for words in the face of an extremely sad death," she said, but she called for caution. "I believe that the grief should not trigger a 'chain of hatred,' " she said.

Across Japan, people reacted with horror to Goto's death, which has brought the distant conflict in the Middle East to a country that still has a pacifist constitution prohibiting it from involvement in foreign conflicts.

Shinzo Abe, the conservative Japanese prime minister who has been trying to put Japan on a more "normal" footing and relax the post-World War II restrictions on the military, said he was "infuriated by these inhumane and despicable acts of terrorism."

"When I think about the unbearable pain and sorrow that his family must be feeling, I am rendered simply speechless," the prime minister said in a statement, which was released in Arabic, in addition to Japanese and English. "Japan will never give in to terrorism," he continued." We will further expand our humanitarian assistance in the Middle East in areas such as food and medical care. Japan will steadfastly fulfill its responsibility in the international community combatting terrorism."

The hostage crisis began three days after Abe, on a visit to the Middle East, announced $200 million in aid for countries who were helping refugees from the Islamic State. The initial ransom demand for Goto and Yukawa was for exactly this amount.

President Barack Obama issued a statement that condemning the "heinous murder of Japanese citizen and journalist Kenji Goto."

"We stand today in solidarity with Prime Minister Abe and the Japanese people in denouncing this barbaric act," the President said in a written statement, according to CNN. "We applaud Japan's steadfast commitment to advancing peace and prosperity in the Middle East and globally, including its generous assistance for innocent people affected by the conflicts in the region."

Bernadette Meehan, a spokeswoman for the United States National Security Council, told the New York Times that American authorities are attempting to verify the latest video's authenticity of the video.

Friends and family remembered Goto as a humanitarian who went out of his way to tell the stories of ordinary people in difficult circumstances.

"Kenji always gave himself up for others and was a remarkable, remarkable man," Goto's friend Mark Tchelistcheff told Sky News. "He reported about humanity, the people on the street. He knew the risks and he took the risks because he thought he could really help. Kenji was not just a good friend to me, he was a friend to the people. The world is a lesser place today with his loss."