TOKYO, Jan. 26-- Japanese Prime Minister Shinzo Abe reiterated his assurance Monday that Japan would use all available means to secure the safe release of Kenji Goto, a war journalist, still held captive by the Islamic State (IS) militants, following the likely killing of Haruna Yukawa, a security contractor, on Saturday.

In a meeting of his Liberal Democratic Party (LDP) lawmakers earlier in the day, Abe said that Japan would cooperate with the necessary countries in a bid to win Goto's release.

"We will use all possible means to win his release by seeking cooperation with other countries," the prime minister said, echoing the words of his top spokesman, Chief Cabinet Secretary Yoshihide Suga, who told an earlier news conference that Japan would use "every channel available" to secure Goto's safe release.

Monday's pledges follow a video released by IS purportedly showing Goto holding the decapitated corpse of Yukawa. The government here has confirmed that the video was "highly likely" to be credible.

An accompanying soundtrack, believed to be Goto's voice, pleads in English for his life and begs for the release of an Iraqi woman, Sajida al-Rishawi, who is being held on death row in a Jordanian prison for her part in the terror attacks on three hotels in Amman in 2005.

The Islamic State militant group's Internet radio service Al- Bayan said Sunday in Arabic that the group has killed one of the two Japanese hostages as per a previous warning issued to Japan.

In a video posted to the popular video-hosting site YouTube on Tuesday, an IS militant initially demanded Japan pay 200 million U. S. dollars for the release of both hostages within 72-hours. The amount demanded by the group was the same as that pledged by Abe in a speech given when the Japanese leader was in Cairo as part of a Middle East tour, which was cut short as the hostage crisis evolved.

During the speech, Abe said that Japan would support global anti-Islamic State efforts and contribute to the countries involved in the campaign. The prime minister also said Japan would provide support to Iraqi and Syrian refugees.

Following the first video being posted online, the Japanese government had been desperately looking into all and every possible channels available to it, to conduct dialogue with the IS militants on the possible release of its two citizens, particularly through connections it has in Jordan, where Japan has set up its emergency headquarters to conduct operations from, including contacting local tribes and religious leaders in the area for assistance.

Abe and a group of his senior advisers spoke to King Abdullah II of Jordan by phone on Saturday, the Foreign Ministry here confirmed, with the prime minister reconfirming on a TV program that human life remained the "top priority."

"We are consulting closely with Jordan from the viewpoint that human life is the top priority," Abe told the public broadcaster NHK on Sunday, while maintaining his stance that such an act of terrorism is "outrageous and impermissible" and has caused him nothing but "strong indignation."

But the killing of Yukawa, a self-styled security contractor from Chiba Prefecture, according to security analysts close to the mater, is evidence that Japan either failed to make contact with the militant group following the first ransom demand, or its negotiating parameters were either too narrow or not acceptable to IS.

Despite the original 72-hour deadline having passed, the analysts said there is still a chance of the second hostage's safe release, as the demands have changed.

"They no longer want money," Goto said in the message. "So, you don't need to worry about funding terrorists. They are just demanding the release of their imprisoned sister Sajida al-Rishawi. It is simple. You give them Sajida and I will be released," said Goto in the recorded message.

But while speculation grows about a possible hostage-prisoner swap, experts have said that there is pressure on Abe and Japan to maintain its vow to not negotiate with terrorists and despite the pledge Japan made along with Group of Eight leaders in 2013 to not pay ransom demands to terrorist organizations in hostage situations, some of Japan's allies expect Abe to adhere to a zero tolerance policy of not negotiating at all with terrorists.

United States President Barack Obama offered his "condolences for the murder" by phone to Abe from Delhi and pledged unwavering "solidarity with the Japanese people," according to a White House statement, which added that the U.S. will work with its ally to " bring the perpetrators of these murders to justice and will continue to take decisive action to degrade and ultimately defeat IS."

For his part, British Prime Minister David Cameron said the beheading of Yukawa and ongoing IS threats are "yet another reminder of the murderous barbarity of these terrorists," adding that Japan was doing the right thing in not bowing to the terrorists demands.

"Britain strongly supports the firm stance Prime Minister Abe and his government have taken," Cameron was quoted by local media as saying.

On Sunday, the UN Security Council in a statement condemned the killing of Yukawa as a "heinous and cowardly act" and demanded the immediate release of Goto.

But while the U.S. and Britain have a zero tolerance policy when it comes to paying ransoms or otherwise negotiating with terrorists, France, for example, has, according to sources with knowledge of the matter paid tens of millions of U.S. dollars to secure the release of its nationals held by IS militants over the years.

And while France has denied the allegations publicly, there are also reports of Japan paying three million U.S. dollars in 1999 for the release of four mining experts held to ransom in Kyrgyzstan.

Beyond using "all possible means" to ensure Goto's safe release, Abe and other high level government officials have yet to officially make a public response to the latest demand from IS.