Israel declared a complete siege of Gaza, increasing airstrikes and sealing it from water, fuel and power supplies on Monday, the Associated Press reported. In response, Palestinian militant group Hamas has threatened to kill a hostage every time attacks targeted civilians in the Gaza Strip without warning.

“We have decided to put an end to this and as of now, we declare that any targeting of our people in their homes without prior warning will be regrettably faced with the execution of one the hostages of civilians we are holding,” said Abu Obeida, the spokesperson of the Qassam Brigades, in an audio released on Monday.

More than 150 Israeli civilians and soldiers have been taken captive, PTI reported. Qassam Brigades is the military wing of Hamas.

Israel’s Minister of Foreign Affairs Eli Cohen warned Hamas against harming the hostages, saying that it was committed to bringing them home. “This war crime will not be forgiven,” said Cohen.

Hamas, which runs Gaza, launched a multi-pronged attack early Saturday by firing a barrage of rockets towards Israeli cities and sending in militants via paragliders and boats.

Israel retaliated with a wave of air strikes on housing blocks, tunnels, a mosque and homes of Hamas officials in Gaza as Prime Minister Benjamin Netanyahu warned of “mighty vengeance”. On Sunday, the Israeli government formally declared war and gave the green light for “significant military steps”.

The toll in the war crossed 1,800 on Tuesday. The Israeli embassy in the United States said that over 998 Israelis have been killed since the conflict erupted, while over 3,400 have been injured. The Palestinian health ministry said that 830 persons have died in Gaza and 4,250 have been wounded, according to Al-Jazeera.

The United Nations has said that the war has resulted in over 1,23,000 people having been internally displaced in Gaza due to concerns about their protection and the destruction of homes.

As Israeli airstrikes hit hundreds of targets, damage to water, sanitation and hygiene facilities has affected over 4,00,000 people, according to the intergovernmental organisation. The Gaza Power Plant is now the only source of electricity and could run out of fuel within days, it warned.

UN Secretary-General Antonio Guterres said that he was “deeply distressed” by Israel’s complete siege on Gaza. “The humanitarian situation in Gaza was extremely dire before these hostilities,” he said. “Now, it will only deteriorate exponentially.”

Meanwhile, Netanyahu said that his country had “only started striking Hamas”. “What we will do to our enemies in the coming days will reverberate with them for generations,” he said.

The Israel military has mobilised 3,00,000 members of its reserve force on the border with Gaza.

“We have never drafted so many reservists on such a scale,” said chief military spokesperson Rear-Admiral Daniel Hagari, reported Reuters. “We are going on the offensive.”

Israeli military forces have reportedly called and sent audio messages to Palestinians, telling them to leave areas mainly in the northern and eastern territories of Gaza.

India firmly with Israel, Modi tells Netanyahu

On Tuesday, Prime Minister Narendra Modi said that he conveyed India’s support for Israel to Netanyahu.

“I thank Prime Minister Benjamin Netanyahu for his phone call and providing an update on the ongoing situation,” Modi said in a social media post. “People of India stand firmly with Israel in this difficult hour. India strongly and unequivocally condemns terrorism in all its forms and manifestations.”