Digital devices and documents retrieved from Hamas militants after the October 7 attack reveal years of planning and a very high level of "detail and readiness", Israeli intelligence officers say.

The material taken from dead or captured Palestinian gunmen show detailed plans for an assault that aimed to cause "such a shock as to break people's spirit", one officer told reporters.

Data from mobile phones, computers, tablets, GPS devices, GoPro cameras, maps and notebooks "show years of planning on how to attack bases and kibbutzim," said another intelligence officer, both speaking on condition of anonymity.

On October 7, hundreds of Hamas and allied Gaza militants stormed into southern Israel, killing more than 1,200 people, mostly civilians, and taking about 240 hostages according to Israeli officials.

In response, Israel vowed to destroy Hamas with relentless bombardment and a ground offensive, killing around 15,900 people, mostly women and children, according to the health ministry in Hamas-run Gaza.

To analyse the material, Israel has reactivated a military intelligence unit called Amshat to plough through the numerous Arabic documents and decipher millions of pieces of electronic data.

Together, they constitute "a battle plan," one officer said. "The level of detail and of readiness are the biggest surprise."

The Amshat unit was founded after the 1973 Arab-Israeli war when Israel was blindsided by Egyptian and Syrian attacks and has been reactivated several times since.

The New York Times reported on December 1 that more than a year ago Israeli intelligence had obtained a Hamas plan giving step-by-step details of an attack similar to October 7, but which was judged to be an "imaginary" scenario.

Hostage-taking manual

Detailed tactical plans were discovered on computers, including objectives, names of the units involved and missions assigned to each of them, together with precise operational details, timings and a list of weapons needed.

There was a detailed hand drawing of the military outpost of Nahal Oz, which Hamas seized.

On the bodies of dead fighters were found satellite photos and precise plans of two of the attacked kibbutzim.

Media reports have already speculated that Palestinians and Israeli Arabs workers may have helped draw up detailed maps of the kibbutzim. But it was not immediately clear where the knowledge of the military base had come from.

The media briefing was also told that "part of the training was on how to take hostages" and that "checklists" and "phrase books" had been found.

The checklist seen by AFP tells militants to cover the eyes and tie the hands of all adult hostages.

It adds that the hostage-takers should "kill those who cause problems or seek to escape".

A conversation guide shown to AFP includes around 50 expressions in Hebrew transcribed phonetically, including "shut up", "don't move", "hands in the air" and "lie down".

Gold nugget

Surprisingly, some documents found were unrelated to the October 7 attack, including several deemed to be of high military value.

"Some of the Hamas fighters were kept in the dark and did not know what would happen," said one officer.

"A lot of them came with things that were not relevant to the raid, some with cars used on a daily basis," said the other.

In the mountain of information, one intelligence officer said, "some things were known, some are new … We have to find the gold nugget".

One officer said that a detailed map of southern Gaza had been found, identifying previously unknown Hamas military installations.

Journalists were also told that Amshat had obtained images of tunnels in Gaza, without being told how these were obtained.

The images showed long corridors, reinforced by concrete and metal, wide and high enough for a vehicle to pass through.

One intelligence officer said they would "not be surprised" if there were more than 500 kilometres (300 miles) of deep, interlacing tunnels in total.

"All of Gaza Strip is a matrix of tunnels… Imagine how many hostages you can put inside."