AMNA NAWAZ: Another of President Biden's priorities during his trip to Israel today, securing the release of hundreds of hostages held in Gaza by Hamas.

As many as 13 are believed to Americans.

In Tel Aviv, special correspondent Willem Marx has the story of one woman with five relatives held hostage and the desperate hours spent to bring them home.

WILLEM MARX: Every Saturday evening throughout this year, thousands of Israelis crowded a traffic intersection in central Tel Aviv to protest Prime Minister Benjamin Netanyahu and his coalition government's attempts to overhaul the country's judicial system.

After Hamas gunmen killed hundreds during attacks on Saturday October 7, there was no protest, only shock and anger.

But outside Israel's Ministry of Defense the following Saturday, much smaller groups once more gathered to grieve and demand government action over dozens of people still missing after the attacks, many assumed to be held hostage by Hamas and other armed groups inside Gaza.

Among the faces on this wall of pain, 12 year old Erez, accompanied by armed men in this video shared on social media the previous Saturday.

ABBEY ONN, Relative of Missing Israelis: American citizens who are being held hostage.

WILLEM MARX: His cousin, Abbey Onn, says she's almost been working too hard to stop and worry, let alone sleep.

ABBEY ONN: I have showered today.

That's good.

WILLEM MARX: Spending all her time talking to governments and groups she hopes can help her, for at the end of Hamas' attack on a kibbutz near Gaza called Nir Oz, five of Abbey's family members were .

ABBEY ONN: There were 400 people that lived on the kibbutz, and there are 160 people that survived.

And they are not among them.

WILLEM MARX: A grandmother named Carmela turned 80 this week.

Her middle aged son-in-law, Ofer, and three of her grandchildren, Sahar, 16, Noya, aged 13, and the youngest, Erez, all vanished.

ABBEY ONN: The messages that we received were messages to say goodbye, that they didn't believe that they would survive what was happening.

And the message that sticks with me the most is from one of the mothers that survived that said this was a holocaust.

WILLEM MARX: Carmela's one of around a dozen Americans the U.S. now says are held in Gaza, their whereabouts an apparent priority for President Biden, who arrived in Israel today, after talking with Abbey and others last week on Zoom.

Right across Israel, hundreds of communities are mourning loved ones killed by Hamas.

But there are some families that face a different kind of anxiety, with their relatives held in Gaza against their will at a time of unrelenting airstrikes on the territory.

ABBEY ONN: The U.S. government up until this point has been unbelievably supportive.

They are working in deep partnership with the Israeli government.

And they are extremely communicative to us, in the sense that we speak everyday to the State Department, to the FBI, and we had a chance to meet yesterday with Secretary of State Blinken.

WILLEM MARX: As part of her campaigning, Abbey's already met with Senate Majority Leader Chuck Schumer, as well as Blinken, during their visits to Israel.

WOMAN: Thank you so much for being here, for speaking to me.

ANTONY BLINKEN, U.S. Secretary of State: And I'm so, so sorry that you have to go through this.

For the families of the missing, there's an unrelenting agony of not knowing the fate of their loved ones, something that I don't think most of us can truly understand, truly contemplate if you're not in their shoes.

ABBEY ONN: It felt like a human interaction.

It didn't feel like a governmental interaction.

It felt empathetic and humane.

And he has deployed his special envoy for hostages to the region to Israel for the foreseeable future.

WILLEM MARX: The bombing in Gaza has already killed thousands of Palestinians.

If Abbey's loved ones are there, she knows it threatens their lives too.

ABBEY ONN: We want civilians out of this.

We understand, on behalf of the Israeli government, there will be a military response.

But we want there to be a diplomatic resolution to the hostage crisis before a ground incursion or continued bombing.

WILLEM MARX: Is that something you think could happen?

ABBEY ONN: I think, if we continue to put pressure, to say their names and continue to speak about hostages, I think it is an awful, awful challenge for the government to figure out how to respond to the terror and save hostages at the same time.

WILLEM MARX: At this moment of massive uncertainty, it's a task several governments are quietly trying to achieve.

For the "PBS NewsHour," I'm Willem Marx in Herzliya, Israel.