Israeli airstrikes continued on Monday as the country’s military called up about 300,000 reservists ahead of a potential ground invasion of Gaza.

Fighting between Israeli soldiers and Islamist Hamas militants continued in the border area with Gaza on Monday, as Israel’s defence minister vowed a “complete siege” of the coastal strip.

United Nations secretary general António Guterres urged restraint, acknowledging “Israel’s legitimate security concerns” but expressing anguish that the “extremely dire” conditions for civilians in Gaza “will only deteriorate exponentially.”

Israeli leaders, however, vowed massive and lengthy retaliation for the deadly attacks on Israel launched by Hamas from the Gaza Strip on Saturday.

Israeli gunships also launched strikes in southern Lebanon, raising fears that the conflict could broaden and escalate further.

Prime Minister Benjamin Netanyahu said Israel’s response “will change the Middle East.”

“What Hamas will face will be harsh and terrible,” Netanyahu said on Monday during a meeting with officials from towns in southern Israel, according to a statement. “We are only at the beginning.”

He called on the opposition to enter an emergency government.

“We are engaged in a mission for our homeland, a war to secure our existence, a war that we will win,” he said in a televised speech.

Netanyahu declared the divisions among Israelis to be over. “We are all united.”

At least 900 Israelis were killed and 2,600 wounded in the Hamas attacks on Saturday in the worst civilian bloodbath in the country’s history, according to the latest count by Israeli authorities.

More than 4,500 rockets have since been fired at Israel, according to official figures.

According to the health ministry there, repeated Israeli strikes on densely populated Gaza killed at least 687 people and left more than 3,800 injured.

Hamas militants took at least 150 people captive and brought them back to Gaza, including women, children and the elderly.

In addition to Israelis, citizens of a number of other countries are believed to be among the captives.

A Hamas spokesman threatened on Monday that the group would execute one hostage for every unannounced Israeli strike on Gaza.

The militant group had offered to trade a number of kidnapped elderly Israeli women for the release of 36 imprisoned Palestinian women held in Israel.

The militant group seized sole control of Gaza by force in 2007.

United Nations spokesperson Stéphane Dujarric said about 13,000 UN employees were in the Gaza Strip, and a further 4,000 staff were in the West Bank.

“They’re obviously not able to leave. They are focused on trying to do whatever they can to help the population within their mandate,” Mr Dujarric said.

The Israeli military, meanwhile, reported that forces had regained control over villages near the Gaza Strip and had stopped the flow of militants across the border, although clashes with Hamas attackers continued in rural areas in Israel.

A military spokesman said on Monday evening that hundreds of Hamas militants had been captured and hundreds more killed in Gaza and along the border fence.

Israel’s army instructed people in the country to stock up on food, water and medicine for at least 72 hours. 

Citizens should also obtain other emergency equipment and check where the nearest air raid shelter is, it said.

On Monday, violence between Israeli forces and Palestinians continued in the occupied West Bank.

According to the Palestinian Health Ministry in Ramallah, three Palestinians, including an 18-year-old who tried to ram a settlement with a tractor, were killed in clashes with the Israeli army.

(NAN)