JERUSALEM: The construction of a new port in Gaza and an accompanying U.S. military-built pier offshore are underway, but the complex plan to bring more desperately needed food to Palestinian civilians is still mired in fears over security and how the humanitarian aid will be delivered.

The Israeli-developed port, for example, has already been attacked by mortar fire, sending high-ranking U.N. officials scrambling for shelter this week, and there is still no solid decision on when the aid deliveries will actually begin.

While satellite photos show major port construction along the shore near Gaza City, aid groups are making it clear that they have broad concerns about their safety and reservations about how Israeli forces will handle security.

Sonali Korde, an official with the U.S. Agency for International Development, said key agreements for security and handling the aid deliveries are still being negotiated. Those include how Israeli forces will operate in Gaza to ensure that aid workers are not harmed.

"We need to see steps implemented. And the humanitarian community and IDF (Israeli Defense Forces) continue to talk and engage and iterate and improve the system so that everyone feels safe and secure in this very difficult operating environment," Korde said.

A senior U.S. military official said Thursday the U.S. is on track to begin delivering aid using the new port and pier by early May. The official, who spoke to reporters on condition of anonymity to discuss details not yet made public, said deliveries through the sea route initially will total about 90 trucks a day and could quickly increase to about 150 trucks daily.

The senior official acknowledged, however, that the final installation of the U.S.-built causeway onto the beach at the port will be governed by the security situation, which is assessed daily. The Israeli Defense Force has a brigade — thousands of soldiers — as well as ships and aircraft dedicated to protecting the deliveries, the official said.

Asked about the recent mortar attack, the miliary official said the U.S. assesses that it had nothing to do with the humanitarian mission, adding that security around the port will be "far more robust" when the deliveries start.

In addition, the U.S. has rehearsed offensive and defensive measures to ensure U.S. troops working at the pier and those on the floating platform several miles off shore are all protected.

Aid groups have been shaken by the deaths of seven World Central Kitchen aid workers in an Israeli airstrike on April 1 as they traveled in clearly marked vehicles on a delivery mission authorized by Israel. The killings have hardened sentiment among some aid groups that the international community should focus instead on pushing Israel to ease obstacles to the delivery of aid on land routes by truck.

The World Central Kitchen staff, who were honored at a memorial service Thursday in Washington, are among more than 200 humanitarian workers killed in Gaza, a toll the U.N. says is three times higher than any previous number for aid workers in a single year of any war.

Development of the port and pier comes as Israel faces widespread international criticism over the slow trickle of aid into the Palestinian territory, where the United Nations says at least a quarter of the population sits on the brink of starvation.

This is how the sea route will work:

— Pallets of aid will be inspected and loaded onto mainly commercial ships in Cyprus, which then will sail about 200 miles to the large floating platform being built by the U.S. military.

— The pallets will be transferred onto trucks, driven onto smaller Army vessels and then taken several miles to the causeway, which will be roughly 1,800 feet, or 550 meters, long and anchored to the shoreline by the Israeli military.

— The trucks will then go down the causeway to a secure drop-off area, where pallets will be distributed to aid agencies. That mission could last several months, the U.S. military official said.

A U.N. official said the port will likely have three zones — one controlled by the Israelis where aid from the pier is dropped off, another where the aid will be transferred, and a third where Palestinian drivers contracted by the U.N. will wait to pick up the aid before bringing it to distribution points.

The construction of the new port in the Gaza Strip appears to have been moving quickly over the last two weeks, according to satellite images analyzed Thursday by The Associated Press. Offshore, U.S. Navy and Army vessels have started the construction of the large pier, or floating platform.

The port sits just southwest of Gaza City, a bit north of a road bisecting Gaza that the Israeli military built during the fighting. The area once was the territory's most-populous region, before the Israeli ground offensive rolled through, pushing over 1 million people south toward the town of Rafah on the Egyptian border.

No militant group immediately claimed responsibility for Wednesday's mortar attack at the port site, and no one was hurt of killed. But it reflected ongoing threats from Hamas, which has said it would reject the presence of any non-Palestinians in Gaza.

High-ranking Hamas political official Khalil al-Hayya told the AP that the group would consider Israeli forces — or forces from any other country — stationed by the pier to guard it as "an occupying force and aggression," and that they would resist it.