U.S. Secretary of State Marco Rubio arrived in Israel on Thursday as part of Washington‘s efforts to normalize the situation in Gaza following the declaration of a cease-fire.

During his remarks on Friday morning, he described coordinating the ceasefire as a “historic mission,” noting that Washington and its partners are working to maintain it, provide assistance and prepare for the entry of the International Stabilization Force, a multinational peacekeeping force, into the Strip.

“This is a historic mission,” he said from the building housing the U.S.-Israel Center for the Coordination of Political and Military Affairs in southern Israel, which oversees the cease-fire in Gaza, adding that the implementation of the plan “will not be a linear path. There will be ups and downs and twists.”

“However, I believe we have many reasons to be optimistic about the progress that has been made,” he added.

Rubio also said there is a growing presence of staff from the US State Department “and related agencies” at the center, which “will continue to grow” to “provide staff in areas such as emergency response and humanitarian coordination.”

He also said that in order to move on to the next phases of the ceasefire plan, the center is focused on ensuring the success of its initial phase. “We need to complete the process that we are currently engaged in, which is to ensure that the ceasefire is maintained without disruption, to ensure that people receive the assistance that they need to survive without being subjected to looting, theft or any other form of diversion, and at the same time to create the conditions for the [International] Stabilization Force to enter as soon as possible to provide the stabilization that we need to move into the next phases of this plan.”

In addition, he said that “on the other side of the yellow line”, in the areas of Gaza from which the IDF withdrew under the terms of the ceasefire, “there is still a terrorist group that remains armed, and we have seen them take action against their own population”, referring to Hamas.

He urged, further, “that more media coverage be given to the fact that Hamas has mistreated the Palestinians, has mistreated the people of Gaza in recent days. This is something that needs to be highlighted.”

Elsewhere in his remarks, Rubio refused to concede that Israel would need US “permission” to resume fighting against Hamas in Gaza if the group continues to pose a threat, and stressed that the US ceasefire plan has broad regional support and is “the best” and “only plan.”

“There is no plan B. This is the best plan. It is the only plan. It’s a plan that we believe can work. It’s a plan that we believe is on the path to success,” he said.

In response to another question about Hamas disarmament, Rubio said that “if Hamas refuses to demilitarize, this will be a violation of the agreement and should be enforced. I will not go into the mechanisms by which it will be imposed, but it will have to be imposed. We are talking about an agreement, and an agreement requires the fulfilment of its terms. Israel has fulfilled its commitments. They are standing on the yellow line, and that depends on demilitarization.”

On the West Bank issue, he estimated that Israel would not proceed with its annexation.