Twenty-two killed and 90 injured as Netanyahu sends tanks to Gaza border, while Hamas fires 140 rockets far into Israel

Israeli jets and naval gunfire pounded the Gaza Strip on Tuesday, killing more than 20 people and injuring dozens more, as the government of Binyamin Netanyahu launched a large-scale military operation against the Islamist militant group Hamas in the coastal enclave.

Israel announced it had authorised the call-up of up to 40,000 reservists for a possible ground operation, even as it began moving convoys of additional tanks and other armour to the Gaza border.

"We have been instructed by the political echelon to hit Hamas hard," General Moti Almoz, the chief military spokesman, told army radio. He said the action would take place in stages.

The announcement came as explosions boomed across the Gaza Strip, sending plumes of grey smoke into the sky and shaking buildings in streets already largely emptied of people.

From the other side, armed factions in Gaza fired about 140 rockets into southern Israel on Tuesday. There were no reports of deaths from the rocket attacks.

The Israeli military, threatening a long-term offensive, hit more than 150 sites and said that Operation Protective Edge aimed to strike Hamas and end the rocket fire that has intensified and reached deeper into Israel in recent weeks.

"We will not tolerate rocket fire on Israel's cities, and we are preparing to expand the operation with everything at our disposal to strike Hamas," said Moshe Ya'alon, Israel's defence minister, who announced a special state of emergency in the south of the country.

In a nationally televised statement, Netanyahu said continued rocket attacks on Israeli communities would not be tolerated.

"Therefore I have ordered the military to significantly broaden its operation against Hamas terrorists and against the other terrorist groups inside Gaza," he said. "I call on you to display patience, because this operation could take time."

The White House condemned the rocket attacks against Israel. "No country can accept rocket fire aimed at civilians and we support Israel's right to defend itself against these vicious attacks," said White House spokesman Josh Earnest.

Mahmoud Abbas, the Palestinian president, called on Israel to halt the airstrikes immediately and appealed for calm. "The Palestinian leadership is conducting intensive and urgent contacts with regional and international parties to stop the escalation," he said.

The Israeli military said on Tuesday night it had foiled an attempt by Palestinian militants in the Gaza Strip to infiltrate southern Israel by sea, the first such infiltration effort in recent memory, a spokesman said. Lt Col Peter Lerner said four attackers were killed after coming ashore on Zikim beach.

After the worst outbreak of violence along the Gaza frontier since an eight-day war in 2012, the Israeli military said a ground invasion of the enclave was possible, though not imminent, and urged citizens within almost 25 miles of the territory to stay close to bomb shelters.

The military said it had struck militant compounds, concealed rocket launchers and other militant infrastructure sites. Most were targeted by airstrikes, and three were attacked from the sea.

In the most serious single incident, seven Palestinians including two children were killed and about 25 wounded in an attack on a house in the Khan Younis area in south Gaza.

Residents said the house belonged to the family of a Hamas member and the casualties occurred when the property came under attack for the second time.

After the first strike people had gathered on the roof of the house as "human shields", hoping their presence would deter a second strike, the residents said. The Israeli military made no immediate comment about the incident.

The military offensive is taking place against a background of rising tensions across Israeli and Palestinian areas following the kidnap and murder of three Israeli teenagers, which Israel blamed on Hamas, and a gruesome killing, believed to be in revenge, by Jewish extremists of a Palestinian teenager last week, which sparked widespread violent protests.

In one strike, three Hamas members from the Qassam brigades were killed in their car at a crossroads in Zarkar, along with two bystanders, residents said. One of those killed was Mohammad Abu Shaban, a senior figure in Hamas's military wing.

As the residents began to describe what had occurred, three further explosions detonated loudly, scattering them.

A strike in the early hours of Wednesday on a house in Beit Hanoun in the north of the Strip killed six people, including a senior leader of the militant group Islamic Jihad. Hafez Hamad, two of his brothers and his parents were killed along with an unidentified woman, Gaza interior ministry said. That brought the death toll since Israel began its offensive to 22: Hamad, four Hamas gunmen and 17 civilians, including seven children.

At Shifa hospital in Gaza City, Ahmad Arafat, 33, and Mohammad Abu Tawilah, 16, were being treated in separate rooms after being caught in a blast in the eastern neighbourhood of Shujai'a.

Speaking through a bloody wad of cotton wool after shrapnel broke his teeth, Arafat, who used to work for the Palestinian Authority but is now unemployed, said he hoped "all of Israel's cities" would be struck by missiles in response to the latest air strikes. "God knows what is going to happen, but I want the resistance to hit Tel Aviv. We need suicide bombings against the Israelis."

In a room a few doors down, Bashir Abu Tawliah was bending over his unconscious son Muhammad, 16, dabbing a dribble of blood from his son's broken nose. "He was with his friends in the street when the strike occurred. They were very close. They weren't involved in firing rockets. What did my son do? What do I want? I want it to escalate. I want them to feel the same pain as we do. Gaza is Hamas. They can't dismantle Hamas without dismantling Gaza."

Israel Defence Forces said on Tuesday night that 117 rockets had struck the country in the past 24 hours and that an additional 29 had been intercepted. Militants twice fired rockets at Tel Aviv, both intercepted by the "Iron Dome" rocket defence system. Hamas said it had fired a salvo of four rockets at Jerusalem, and two distant booms could be heard from the city's centre, but police reported no injuries.

The army was also checking reports that rockets had flown north of Tel Aviv, which would be the deepest strikes ever carried out by Hamas.

Netanyahu at first seemed unwilling to be drawn into a prolonged and bloody conflict over Gaza, offering "quiet for quiet" if Hamas halted its rocket fire. But the death of six Hamas members in an explosion in a tunnel on Monday prompted immediate threats of retaliation and escalation of rocket fire.

Hamas, which has been badly hit by an Egyptian blockade that has closed the Rafah tunnels and halted the flow of goods and funds into the strip, might believe it could gain from a prolonged conflict – as the group did after Operation Cast Lead, the 2009 invasion of Gaza.

"We have repeatedly warned Hamas that this must stop and Israel's defence forces are currently acting to put an end of this once and for all," said Netanyahu's spokesman, Mark Regev.