Israel has spent over one billion shekels (some $250 million) since 2004 trying to thwart Hamas tunneling under the Israel-Gaza border, an Israeli TV report said Friday night.

The money has gone toward developing technology to discover the locations of such tunnels and unspecified “operational efforts,” Channel 2 news said.

It quoted Israeli military sources saying the effort to counter Hamas’s under-border tunneling was a “central” priority for the IDF.

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The TV report’s reference to 2004 was not immediately clear. Israel controlled the Gaza Strip until 2005, when it dismantled more than 20 Jewish settlements there, removing all of their approximately 8,000 residents, and withdrew its military forces. Hamas, an Islamist terror group openly committed to destroying Israel, seized full control of Gaza from Mahmoud Abbas’s Palestinian Authority in 2007.

The Friday TV report came against the background of rising complaints from residents of southern Israel, who claim to hear and feel Hamas tunneling beneath their communities. Hamas leaders have bragged recently that the attack tunnels, some 30 of which were destroyed by Israel in the 50-day war of summer 2014, have been rebuilt and again stretch into Israel.

The past few weeks have seen at least five separate tunnel collapses in the Gaza Strip, according to Palestinian reports, and about 11 deaths of Hamas tunnelers.

Asked about those incidents last week, IDF Maj. Gen. Yoav Mordechai, head of the Coordinator of Government Activities in the Territories, refused to say whether Israel was involved. “God knows,” he said, according to the Palestinian Ma’an news agency. “I would suggest the residents of the Gaza Strip not to occupy themselves with the tunnels and to get away from them, especially after seeing the results in recent days,” he added.

The IDF’s Chief of Staff Gadi Eisenkot said on Tuesday that the army was working, mostly in secret, to counter the Gazan tunnel threat and has recently been employing nearly 100 engineering vehicles on the border to locate and destroy the Hamas passageways.

He also said the option of a preemptive strike was “being discussed in the places where it needs to be discussed.”

“We have advanced capabilities,” Eisenkot said, presumably referring to tunnel detection systems that Israel has been rumored to be developing in response to the underground threat from Gaza. “We are doing a lot, but many of [the things we do] are hidden from the public. We have dozens, if not a hundred, engineering vehicles on the Gaza border,” Eisenkot added.

The army chief was responding directly to criticism lodged against the IDF in the draft of a report by State Comptroller Yosef Shapira last week. “The draft as submitted points to gaps and failures, some severe, in the readiness for the tunnel threat and dealing with them,” the comptroller’s office said in a statement.

Prime Minister Benjamin Netanyahu and Defense Minister Moshe Ya’alon recently rejected a call by Education Minister Naftali Bennett for a preemptive Israeli move to destroy Hamas’s tunnel network, it was reported last week.

“We are working methodically and calmly against all threats, including threats from Hamas, both with defensive and offensive measures. And of course, in the event we are attacked from tunnels in the Gaza Strip, we will act very forcefully against Hamas, and with much more force than Operation Protective Edge,” Netanyahu told a conference of Israeli diplomats two weeks ago.