United Nations Secretary General Ban Ki-moon expressed “alarm” Saturday at Hamas’s pledge the day before to keep building attack tunnels from Gaza into Israel and to advance the development of rockets to fire at the Jewish state.

Ban’s remarks came days after he prompted furious criticism from Israel for remarks that the Jewish state allegedly legitimized Palestinian terrorism.

In a statement issued by his spokesperson, the UN chief said remarks and actions like those undertaken by Hamas do “serious disservice” to Gaza’s population, and endanger efforts to rebuild the coastal enclave devastated in three rounds of fighting between Israel and Hamas since 2008.

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“Such statements and actions put at risk reconstruction, humanitarian and development efforts by the international community and Palestinian and Israeli authorities. They also do a serious disservice to the long-suffering people of Gaza,” said Ban.

The UN chief also reiterated “his condemnation of terrorism in all its manifestations,” a reference to a row that erupted earlier in the week, when he drew fire in Israel for stating that the current wave of Palestinian violence could be rooted in “frustration.”

Ban’s comments came a day after Hamas senior official Ismail Haniyeh told Gazans that “heroes” from the group are tirelessly digging tunnels designed for use in attacks on Israel. He was speaking at the Gaza City funerals for seven excavators killed this week when the tunnel they were working on collapsed due to heavy rains and floods.

Haniyeh also vowed that the group is growing stronger, and would use any means at its disposal to prepare for its next confrontation with Israel, Army Radio reported.

“Some believe that the calm, when the noise of the cannons fall silent, is intended for rest. But the [Izz ad-Din] al-Qassam Brigades continue with their campaign through preparation and training,” said Haniyeh, referring to the Hamas military wing. The resistance, he said, is permanently in a state of continuous preparation.

“East of Gaza City, heroes are digging through rock and building tunnels, and to the west they are experimenting with rockets every day. The resistance continues on its path of liberation of the land,” Haniyeh said during the funerals at the Great Omari Mosque in Gaza City.

Haniyeh’s remarks come at a time of renewed focus on the tunnels in Gaza, with Israel accusing Hamas of reconstructing them following its 2014 war with Palestinian militants in the enclave when many were destroyed.

Gaza has remained largely calm since a wave of Palestinian knife, gun and car-ramming attacks began in October in the West Bank, Jerusalem and across Israel, though a number of people have been killed by Israeli forces during violent protests along the Gaza border.

Ban sparked Israeli outrage Tuesday with his comments about the terror attacks of the past four months, in which more than 25 Israelis have been killed, by saying it was “human nature to react to occupation.” Prime Minister Benjamin Netanyahu on Tuesday accused the United Nations chief of “stoking terror.”

On Wednesday, Ban criticized Israel’s “stifling” occupation of the Palestinian territories.