The tunnel is electrified with the help of solar panels, said Israeli forces.
Former Israel Prime Minister Ehud Barak on Monday said his country had built some of the bunkers beneath Gaza's war-torn Al Shifa Hospital, which has been in the news this past week after Israeli forces said they found a 55-metre "terrorist tunnel" the Hamas had used as a command outpost.
The ex-PM suggested the underground space had been built by Israel "many decades ago" - most probably when Tel Aviv occupied Gaza - "to enable more space for operation of the hospital".
Speaking to CNN journalist Christiane Amanpour, Mr Barak said "it is already known for many years that they (the Hamas) have bunkers originally built by Israeli constructors underneath Al Shifa".
"... was used as Hamas command outpost... it was at junction of several tunnels (that were) part of this system. I don't know to what extent it is 'major'... probably not only command outpost... there are others under other hospitals or sensitive places, but for sure it was used by Hamas," he said.
Pressed by Ms Amanpour on whether he misspoke, Mr Barak clarified, "No... you know, many decades ago we were running the place, four decades ago... so we helped them to build these bunkers to enable more space for operation of hospital, within limited size of the compound."
In 2009, Israeli news outlet Haaretz said that in the 1980s Tel Aviv had expanded the Al Shifa Hospital - built in the late 1960s, when Gaza was under Egyptian rule - compound to include a "large cement basement that housed the hospital's laundry and various administrative services".
Mr Barak suggested the Hamas may have since expanded and linked it to other tunnels and bunkers.
Mr Barak also stressed that because of the "cautious" approach to storming the hospital - which was first surrounded by Israeli tanks as it was starved of food, fuel, water and medicines - Hamas operatives had time to erase, to a large extent, traces of their activities beneath the medical facility.
"We warned for many days we are going to come here. Then we came, very cautiously, in order to avoid loss of lives among doctors, patients... as a result Hamas had all the time in the world to try to make it less apparent that it (the bunker) was in use. But we are confident that for years it was used... as major or non-major... command outpost for Hamas activities," he told the CNN anchor.
Israel has repeatedly accused Hamas of building a command centre in a tunnel network underneath Gaza City's largest hospital - a claim the US says its own intelligence supports but Hamas denies.
Hamas has acknowledged it has a vast network of secret tunnels, bunkers and access shafts throughout the Palestinian enclave, but has denied these are in civilian infrastructure like hospitals.
READ | "Inhuman, Bodies Everywhere": Horror At Gaza Hospital, 179 In Mass Grave
Last week, Israel released footage of the tunnel entrance - located near what they said was a Hamas operative's house and fortified with an explosives-proof door - and bunkers beneath the hospital.
READ | Hamas Tunnel, Body Of Hostage: What Israel Claims It Found At Gaza Hospital
The Israeli military also released photographs of weapons it said it had found inside the tunnel and bunkers; these were dismissed by the Hamas as "lies and cheap propaganda", Reuters reported.
There is still no independent confirmation that the areas beneath the hospital were a Hamas command outpost but, as international media point out, Israel will want to establish this as 'fact' to counter growing pressure to cease military operations in which over 10,000 people have already died.
Meanwhile, Gaza woke Wednesday to a measure of good news.
READ | Israel Agrees To Deal For Release Of 50 Hostages, Hamas Welcomes 'Truce'
Israel and Hamas have agreed to a four-day truce that will see the latter release at least 50 hostages - women and children. The truce is also expected to see 150 Palestinians released from Israeli jails.
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