The Palestinian Islamic Jihad (PIJ) released a video on Tuesday reportedly showing an Israeli hostage alive and held in the Gaza Strip.
The captive, identified by Israeli media as Sasha Trupanov, 28, can be seen speaking in Hebrew in the 30-second clip.
The Hostages and Missing Families Forum campaign group identified him as Alexander (Sasha) Trupanov and called on the Israeli authorities to secure the release of all captives held in Gaza, which has been under Israeli bombardment for almost eight months.
It was unclear when the footage, in which he is seen wearing a T-shirt, was taken.
Trupanov, a Russian-Israeli dual national, was captured on October 7 from Kibbutz Nir Oz along with his mother, grandmother and girlfriend.
The three women were freed during a truce between Hamas and Israel at the end of November, which led to the release of 105 hostages.
"Seeing my Sasha on television today is very heartening, but it also breaks my heart that he has been in captivity for such a long time," said his mother, Yelena Trupanov, in a short message published by the families' forum.
Israel's government has instructed its negotiating team to continue talks with mediators to secure a deal for the release of the hostages, but no new round of talks has begun.
Israel has repeatedly rejected Hamas' demands to end the war in Gaza and completely withdraw from the enclave. Additionally, Netanyahu's cabinet has come under intense criticism from Israelis for failing to secure the release of hostages.
"The Israeli government must give a significant mandate to the negotiating team, which will be able to lead to a deal for the return of all the hostages - the living to rehabilitation and the murdered to burial," a families' forum statement said after the release of Trupanov's video.
Israel's military offensive in Gaza has killed at least 36,171 people, mostly women and children, according to the territory's health ministry.
Israel's actions in the enclave have been labelled as genocide by many global leaders.