In Beit Hanoun, where his forces were operating, some gunmen had stormed the Israeli military from tunnel shafts and had been killed, he said.
"We don't want to go down there. We know that they left us a lot of side-bombs (improvised explosives devices)," he said.
One such bomb, rigged to the cover of a tunnel-access shaft at ground level, had killed four special forces reservists last week.
Destroying a shaft is relatively easy and quick, the officer said, adding: "Any platoon can do it."
The tunnels are harder to tackle. The officer said several tonnes of the exploding gel - on which he declined to give any technical details, other than to say it is brought in by truck - are required for every few hundred metres of tunnel.
..... sometimes a secondary explosion set off by a tunnel destruction blast "will bring down a building a few hundred metres away".
"It's hard to say how many tunnels (are destroyed) because they are all connected," he said.
One of a handful of hostages released said she and at least two dozen others had been
held in a tunnel. The army officer said care was being taken not to endanger tunnels that may contain hostages.
Palestinian gunmen taken captive have provided Israel with intelligence on the tunnel network, he said, but this information has been limited.
With mapping robots and blast gel, Israel wages war on Hamas tunnels