Family Member of Israeli Hostage Advocates For Release, 'Time Is of the Essence'

Omri Miran is among the Israeli hostages being held captive by Hamas ... and his brother-in-law, a former captain in the Israel Defense Forces, is calling for his safe return ASAP.

Moshe Lavi, the former IDF captain, says Omri was held at gunpoint by Hamas terrorists on Oct. 7, when he was kidnapped from his home in Kibbutz Nahal Oz. Moshe says Omri's wife, his sister Lishay, and the couple's 2 daughters, Roni and Alma, were also held at gunpoint with Omri before ultimately being left behind and rescued by the IDF.

Some hostages have since been released by Hamas, but Omri was not among them ... so Moshe and family members of other hostages are pressuring public officials in Israel and across the globe to do whatever is necessary to bring more hostages home.

Moshe tells TMZ ... his family hasn't received any official word of how Omri is doing in captivity, though hostages released 2 weeks ago claimed Omri was seen alive in one of the Hamas tunnels in Gaza.

Still, Moshe says just because Omri was said to be safe back then doesn't mean he's in good shape now ... as Moshe points out, "Every second in captivity is eternity" ... which is why time is of the essence here.

Of grave concern to all the families is the fact 3 of the remaining hostages were accidentally killed during IDF efforts to take out Hamas militants. The victims have been identified, and Omri is not among them.

But, Moshe is calling on public officials to work day and night to bring Omri and his fellow captives back safely to their loved ones.