TEL AVIV (Reuters) - Hamas rockets forced the closure of the main crossing point for humanitarian aid from Israel to Gaza on Tuesday, holding up the transfer of more than 100 truckloads of food and medical supplies including anesthetics, Israeli officials said.

Palestinians wait to receive food supplies from the United Nations Relief and Works Agency (UNRWA) headquarters in Rafah in the southern Gaza Strip November 20, 2012. REUTERS/Ibraheem Abu Mustafa

Despite the fact its air force is bombarding the coastal enclave, Israel is trying to maintain the essential daily flow of basic foodstuffs into the Gaza Strip where most of 1.7 million Palestinians are dependent on aid.

A Twitter message from the Israel Defence Forces (IDF) said that “120+ trucks of supplies from Israel are waiting at Gaza border crossing. Hamas is firing rockets at the crossing. Trucks can’t enter now”.

Israel says it launched its military offensive a week ago to halt increasing Islamist militant rocket fire on southern Israeli communities close to the Gaza Strip.

The Kerem Shalom crossing at the extreme south of the Israel-Gaza border, next to Egyptian territory, is the only freight passage into the blockaded territory.

No comment was available from Hamas. But a Palestinian liaison official said the crossing was closed after some mortar bombs landed at Kerem Shalom and work was suspended after just one hour of operations. The western-backed Palestinian Authority liaises with Israel on Kerem Shalom transfers.

For security reasons, it operates on a back-to-back system: trucks go in from Israel and offload within the protective concrete walls of the terminal, then trucks come in from the Gaza end and load up.

Since the start of the latest round of violence, now in its seventh day, Israel’s Coordinator of Government Activities in the Territories (COGAT), says it has let in 123 trucks loaded with food, medicine and fuel, including 43 that passed on Tuesday before rockets started to fall.

The rest of the transfer included 16 truckloads of medical equipment “specifically vital equipment, such as medicines, anesthetics and disposable medical equipment”, COGAT said.

The main Israeli fortified crossing-point at Erez was opened to permit the exit of 26 patients and their escorts into Israel in order to receive medical treatment, the authority added.

“While Israel is committed to providing continued assistance, it is subject to the limitations created by continuous rocket fire and attacks on the part of Hamas and other extremists groups in Gaza,” COGAT said.

“Rocket attacks endanger the staff manning the crossing and often hinder or prevent the transfer of goods,” it added.

The United Nations Relief and Works Agency for Palestinian Refugees (UNRWA) says 1.2 million Gazans rely on UNRWA assistance, which enters the territory via Israel.

“UNRWA will continue to provide food aid to more than 800,000 refugees in the Strip. Our schools are providing a place of safe shelter. Our health clinics remain open and ready to bring medical care to the children, the sick, and the elderly,” the agency said in its latest update on the crisis.

In relatively normal times about 130 truckloads of aid -- mainly bulk staples -- go through the Kerem Shalom crossing daily.