Israeli forces are "systematically" blocking access to people in need in Gaza, complicating the task of delivering aid in what has become a lawless war zone, the UN said Tuesday.

It has become nearly impossible to carry out medical evacuations and aid deliveries in northern Gaza and increasingly difficult in the south, said Jens Laerke, spokesman for the United Nations humanitarian agency OCHA.

All planned aid convoys into the north have been denied by Israeli authorities in recent weeks, with the last allowed in on January 23, according to the World Health Organization.

Making matters worse, even convoys cleared in advance with Israeli authorities have repeatedly been blocked or come under fire.

Laerke pointed to an incident last Sunday when a convoy, jointly organised by the WHO and the Palestinian Red Crescent (PCRS), to evacuate patients from the besieged Al Amal hospital in the southern city of Khan Yunis, was blocked for hours and paramedics detained.

"Despite prior coordination for all staff members and vehicles with the Israeli side, the Israeli forces blocked the WHO-led convoy for many hours the moment it left the hospital," Laerke told journalists in Geneva.

"The Israeli military forced patients and staff out of ambulances and stripped all paramedics of their clothes," he said, adding that the convoy, which was carrying 24 patients, remained blocked for seven hours.

"Three PRCS paramedics were subsequently detained, although their personal details had been shared with the Israeli forces in advance," Laerke said, adding that just one had been released so far.

"This is not an isolated incident," he stressed.

"Aid convoys have come under fire and are systematically denied access to people in need."

Such "inadequate facilitation for the delivery of aid throughout Gaza means that humanitarian workers are subject to unacceptable and preventable risk of being detained, injured or worse", Laerke said.

Militants also took about 250 Israeli and foreign hostages, 130 of whom remain in Gaza including 31 presumed dead, according to Israel.

Israel's military campaign has killed at least 29,878 people in Gaza, mostly women and children, according to the Hamas-ruled territory's health ministry.