* Secret passage built after 2014 conflict - Israeli army

* Hamas says it is "drop in the sea" of its preparations  

Since being blindsided by Hamas tunnel raiders during the war, Israel has, with US help, stepped up work on technologies for spotting the secret passages. Some Israelis who live on the Gaza frontier believe militants are digging fresh tunnels and worry the counter-measures will come too late.

The tunnel made public on Monday was discovered days earlier but kept under wraps by Israel as it probed what it said were hundreds of metres of shafts on the Israeli side of the border along the southeast of the Gaza Strip. The network was then razed.

Prime Minister Benjamin Netanyahu credited "a world-first breakthrough in tunnel-locating capabilities" for the find but indicated more work was need to complete the counter-measure.

"The government has invested a huge fortune in thwarting the tunnel threat. This is an ongoing effort. It does not end overnight," he said in a TV statement.

Commentary on Israel's Army Radio said the effectiveness of the system announced by Netanyahu should be gauged only once several more tunnels are discovered.

An Israeli military spokesman, Lieutenant-Colonel Peter Lerner, said the tunnel was mostly built after the Gaza war, during which 12 soldiers were killed by Hamas gunmen who burrowed across the border on four occasions.

Hamas's armed wing, which has largely held fire since the war, implicitly claimed the tunnel as its own and said it was "only a drop in the sea of what the resistance has prepared".

Israel has signalled the mere existence of a tunnel - as opposed to its use for an attack - may not be a casus belli.

"We do not seek conflict, but if Hamas tries to provoke the State of Israel and disrupt the lives of residents of the Gaza periphery communities, it will be dealt a very strong blow," Defence Minister Moshe Yaalon said in a statement on Monday.

The Gaza war killed more than 2,100 Palestinians and devastated parts of the enclave. Gaza medical sources and UN officials say most were civilians, a figure disputed by Israel, which lost 67 troops and six civilians to the fighting.

The Gaza periphery is now mostly quiet, except for occasional Palestinian rocket attacks Israel says were carried out by Islamist groups that view Hamas as too lenient.

Israeli security sources say a half-dozen classified anti-tunnel technologies have long been under development though held up by funding problems that were partly alleviated by a US research grant of $40mn this year.