Two multi-storey buildings in Gaza have been completely destroyed by Israeli air strikes in less than 24 hours, possibly signalling a new tactic in Israel’s military campaign.

A 12-storey apartment building in Gaza City was brought down on Saturday evening and a seven-floor office building in Rafah was razed early on Sunday.

The hits followed warnings by the Israel Defence Forces, in leaflets, text messages and automated phone calls. The text of a leaflet dropped from aircraft said: “The IDF intends to attack terrorists and terror infrastructure across the Gaza Strip … Israel is currently attacking, and will continue to attack, every area from which terror activities against Israel originate. Every house from which militant activity is carried out, will be targeted. For your own safety, prevent terrorists from utilising your property for terror agendas, and stay away from every site in which terrorist organisations are operating.”

It was signed “Beware – Israel Defence Forces”.

In the Gaza City strike a huge fireball followed by a black column of smoke rose into the sky after two Israeli missiles toppled the Zafer Tower, one in a group of several highrises in the area. Neighbouring buildings shook from the blasts.

The Israeli military said the missiles targeted a Hamas operations room in the building but did not explain why the entire tower with 44 apartments was brought down.

Gaza police said a warning missile had been fired five minutes earlier and some residents were able to rush out of the building in time. But 22 people were wounded, including 11 children and five women, according to Gaza hospital officials.

Maher Abu Sedo, an area resident, said the two strikes came within seconds of each other.

“The state of Israel has resorted to madness. In less than a minute 44 families have become displaced … They lost everything, their house, their money, their memories and their security”

In total around 100,000 Gazans have become homeless, with more than 17,000 homes destroyed or damaged beyond repair, according to UN figures. However Saturday’s strike marked the first time an entire apartment highrise was destroyed.

In Rafah, in the south of the Gaza Strip, a seven-floor office building was destroyed and a two-storey commercial building with dozens of shops severely damaged, Gaza police said.

An office of the Hamas-run interior ministry was located in the seven-storey Zourab building. Police said seven people were wounded by the bombing of the commercial centre.

More than 100 rockets were fired from Gaza on Saturday, according to Israeli sources. On Friday a mortar shell killed a four-year-old boy in a kibbutz close to the Gaza border. Daniel Tragerman was due to be buried on Sunday morning.

Hamas executed four more alleged collaborators on Saturday, bringing the total to 25.

According to reports, the four were shot dead in Jabaliya refugee camp in Gaza City in front of scores of spectators. Hamas said the men were convicted on evidence brought before a trial, but it withheld their names to protect their families.

Palestinian and international human rights organisations have condemned the wave of summary executions.

Israeli media said a large numbers of residents of southern Israeli communities near the Gaza border were leaving their homes and heading for safer areas following the boy’s death. “I say whoever can leave, whose presence is not crucial should leave,” said minister of public security Yitzhak Ahronovich.

Meanwhile the Israeli military said five rockets were fired from Syria at the Israeli-annexed Golan Heights, falling in open areas, in the early hours of Sunday.

On Saturday at least two rockets were fired from southern Lebanon towards Israel, Lebanon’s national news agency and security sources said, without saying who had launched them.

The Palestinian president, Mahmoud Abbas, and Egyptian officials called on both sides to resume talks aimed at an agreed ceasefire to end the conflict in Gaza. Abbas, in Cairo after meeting President Abdel Fattah al-Sisi, also urged a swift resumption of negotiations.

A senior Egyptian diplomat said Abbas had informed Sisi that Hamas was prepared to come to Cairo for further talks, but Hamas did not immediately confirm the report. Israel also had no immediate comment.

The Egyptian diplomat said Cairo expected to receive responses from both Israel and Hamas by Monday.

Hamas has said it will not stop fighting until the Israeli-Egyptian blockade on Gaza is lifted.

Both Israel and Egypt view Hamas as a security threat and are reluctant to make sweeping concessions without guarantees weapons will not enter the economically crippled enclave.