London, March 19 (Reuters) - Extreme food shortages in parts of the Gaza Strip have already exceeded famine levels, and mass death is now imminent without an immediate ceasefire and surge of food to areas cut off by fighting, the global hunger monitor said on Monday.

The Integrated Food-Security Phase Classification (IPC), whose assessments are relied on by U.N. agencies, said 70% of people in parts of northern Gaza were suffering the most severe level of food shortage, far exceeding the 20% famine threshold.

The IPC said it did not have enough data on death rates, but estimated residents would be dying at famine scale imminently, and children under four may already be.

"The actions needed to prevent famine require an immediate political decision for a ceasefire together with a significant and immediate increase in humanitarian and commercial access to the entire population of Gaza," it said.

In all, 1.1 million Gazans, around half the population, were experiencing "catastrophic" shortages of food, the worst category, with around 300,000 in the areas now facing the prospect of famine-scale death rates.   The prospect of a manmade famine in Gaza has brought the strongest criticism of Israel from Western allies since it launched its war against Hamas militants following their deadly attack on Israeli territory on October 7th.

"In Gaza we are no longer on the brink of famine, we are in a state of famine, affecting thousands of people," EU foreign policy chief Josep Borrell said at the opening of a conference on humanitarian aid for Gaza in Brussels.  "Starvation is used as a weapon of war.  Israel is provoking famine."

U.N. Secretary-General Antonio Guterres called the IPC report an "appalling indictment" and said Israel must allow complete and unfettered access to all parts of Gaza.  "This is an entirely manmade disaster — and the report makes clear that it can be halted."

In the ruins of Gaza City, the main settlement in the north of the Gaza Strip, Israeli forces launched a major assault on Al Shifa hospital overnight.  Once the Gaza Strip's biggest hospital, it is now one of the only medical facilities still even partially functioning in the north of the territory.

Israel said it had killed 20 Hamas fighters, including a senior Hamas commander, Fayeq al-Mabhouh, in the hospital. Hamas confirmed his death in a statement and said he was a Palestinian police official tasked with overseeing the protection of aid deliveries in Gaza.