UNITED NATIONS, United States (AFP)— UN Secretary-General Antonio Guterres on Monday condemned the Hamas attack against Israel but said he was “deeply distressed” by the country’s subsequent imposition of a total siege on the Gaza Strip.

“The humanitarian situation in Gaza was extremely dire before these hostilities,” Guterres told reporters. “Now it will only deteriorate exponentially.”

Earlier in the day, Israeli Defence Minister Yoav Gallant said his country would impose a “complete siege” on the long blockaded enclave and stressed what this meant for its 2.3 million people: “No electricity, no food, no water, no gas — it’s all closed.”

Palestinians in the impoverished coastal territory braced for what many feared will be a massive Israeli ground attack aiming to defeat Hamas and liberate hostages.

“This most recent violence does not come in a vacuum,” Guterres stressed. “The reality is that it grows out of a long-standing conflict, with a 56-year long occupation and no political end in sight.”

“While I recognise Israel’s legitimate security concerns, I also remind Israel that military operations must be conducted in strict accordance with international humanitarian law,” Guterres said.

Following the Islamist group’s unprecedented ground, air and sea attacks, Israel has counted over 700 dead and launched a withering barrage of strikes on Gaza that have raised the death toll there to 560 people.

Guterres began his speech by expressing “utter condemnation of the abhorrent attacks by Hamas and others against Israeli towns and villages in the Gaza periphery.”

“I recognise the legitimate grievances of the Palestinian people,” Guterres said. “But nothing can justify these acts of terror and the killing, maiming and abduction of civilians.”

Israel, which has long prided itself on a high-tech military and intelligence edge in its many conflicts, has been shaken to the core by Hamas’ surprise attack.

The militant group surged into Israeli towns on Saturday, storming military bases, spraying gunfire at civilians and dragging off about 100 hostages.

The conflict has only escalated since then, prompting Israel’s promise Monday to cut off supplies to the region.

“I am deeply distressed by today’s announcement that Israel will initiate a complete siege of the Gaza Strip, nothing allowed in — no electricity, food, or fuel,” Guterres said.

The UN will continue efforts to provide aid to respond to needs in Gaza, Guterres said.

“Israel must see its legitimate needs for security materialised — and Palestinians must see a clear perspective for the establishment of their own state realised,” Guterres added.