Trump hints at 'action' if Hamas doesn't return hostage bodies

Secretary of State Marco Rubio has named U.S. Ambassador to Yemen Steven Fagin as the "civilian lead" of the Civil-Military Coordination Center, in charge of monitoring the ceasefire in Gaza.

Fagin, will join the military lead for the operation, Lt. Gen. Patrick Frank, and 200 servicemembers from U.S. Central Command -- with expertise in transportation, planning, security, logistics and engineering -- who are staffing the hub.

Frank briefed Rubio today at the center, according to the television pool.

Rubio promised more diplomats would arrive at the hub, as well as personnel from partner nations who are involved in shoring up the ceasefire between Israel and Hamas.

Trump Administration officials said the hub will have representatives from partner nations, NGOs, international institutions and the private sector to support stabilization efforts.

Secretary of State Marco Rubio told reporters that Israel's government vote this week to annex the West Bank would "threaten" the peace process, saying it was not a serious effort but rather one deployed to "embarrass Netanyahu, while the vice president was here."

"Right now, if that were to happen, a lot of the countries that are involved in working on this probably aren't going to want to be involved in this anymore. It's a threat to the peace process and everybody knows it," Rubio said.

Rubio remained bullish about the ceasefire agreement but recognized the parties were at the "first mile in a very long journey."

The secretary of state was clear that an end state with an armed Hamas would not be acceptable.

"If Israel's security is threatened, if five years from now, three years from now, two years from now, Gaza is a place where people who want to destroy Israel are able to operate from with impunity, there's not going to be peace," Rubio said.

"If Hamas refuses to demilitarize, it will be a violation of the agreement, and that will have to be enforced," he said.

Rubio made a visit to the U.S.-established Civil-Military Coordination Center on his final day in Israel, where he expressed "healthy optimism" that the growing center can monitor the ceasefire and deconflict as needed to reach an enduring peace in Gaza.

-ABC News' Mariam Khan and Chris Boccia

While aid being allowed into Gaza has increased, it is still falling well short of what is needed to meet the needs of Palestinians in Gaza, World Health Organization Director-General Dr. Tedros Adhanom Ghebreyesus said Thursday.

"There is an increase in amount after the ceasefire, but what is entering Gaza is significantly below the required target ... So if the aid that's entering Gaza is significantly low, it cannot dent the hunger level and the situation still remains catastrophic, because what's entering is not enough," he said.

What is being allowed into Gaza is only meeting the "tip of the iceberg," he told reporters.

"Currently, you have Kerem Shalom and Kisufim crossings, which are open, and where supplies are flowing into Gaza, but too few supplies; Rafah remains closed for people and supplies. So it's vital that Rafah is urgently reopened," he said

"The Rafah crossing was supposed to be opened last week. A significant amount of aid has built up at Al-Arish in Egypt that's ready to enter Gaza as soon as the crossing is opened," he said.

As a fragile ceasefire continues to hold, retired Israel Defense Forces Major General Giora Eiland expressed concern that the deal will fall apart because its unlikely Hamas will be ready to give up its weapons, he told ABC News.

“I don't think that Hamas will be ready to give up its weapons. They might be ready to give up some symbolic positions as a government, but they will never be ready to give up their weapons. That's why I don't believe the Trump plan will successfully be accomplished," he said in an interview in Tel Aviv.

However, under U.S. pressure, Israel is obliged to give the plan a go, but the only part that really matters for Israel is the "demilitarization" of Gaza, he said.

“We have to give a chance because this is American plan and as far as Israel is concerned, if it does work then it is good for us. But I personally don't believe that it will succeed," he said.

The former IDF general believes that Israel should ensure that there is no reconstruction in Gaza unless “this process of demilitarization is accomplished successfully.”

Such a process should, he says, involve destroying all the tunnels, something which a Hamas ambush on IDF troops on Sunday proved has not been completed. Eiland said dismantling Hamas militarily is possible but believes that task now falls to Arab partners of the U.S.

However, Eiland believes Hamas, as a political force, will remain in Gaza.

"You cannot dismantle the sentiment of Hamas which is deep in the hearts and the minds of the people of Gaza. But you can destroy the military abilities," Eiland said.

-ABC News' Tom Soufi Burridge