Mohammed Deeb took the telephone call seriously and told his family and neighbours to get out of the building. An hour later, an Israeli helicopter fired three missiles at the four-storey building in Gaza City, destroying the ground floor and damaging the upper storeys.

Mr Deeb was on the receiving end of a new Israeli tactic of using telephone, radio and leaflets to warn Gazans of impending attacks. The army claims it is an attempt to minimise civilian casualties, but Palestinians say it is a new way of terrorising the population.

Raji Serrani, the director of the Palestinian Centre for Human Rights (PCHR), which has collected several examples of the tactic, described it as "psychological warfare", adding: "Since when did Israel feel the need to warn people that they were about to bomb their homes? They are simply playing with people's minds and inflicting a new panic in Gaza."

The family of Ibrahim Mahmoud in the Bureij refugee camp in central Gaza were ordered to leave their home by an Israeli intelligence officer. The officer called back one hour later to say she had made a mistake. She ended her call to Mr Mahmoud by telling him to "be safe", he told the Associated Press.

The warnings, which sometimes are followed by an Israeli attack and sometimes not, are happening as Israel continues its latest invasion of the Gaza Strip. Four people were killed and dozens injured yesterday as Israeli tanks patrolled residential areas to the east of Gaza City. Twenty-five people were killed on Wednesday.

Fears that Israel will destroy homes are widespread: 900 residents of the al Nader towers, a complex of 12 apartment blocks in the north of Gaza, fled on Tuesday after 10 Israeli shells landed close to them, killing three residents. According to the PCHR, Israel had also informed Palestinian police that they planned to demolish the towers.

Izzat al Jamal, 38, a Palestinian policeman, moved his wife and eight children out of their apartment to emergency accommodation in a local school. "When they started firing, it was clear it was aimed directly at us and it wasn't a random mistake. I had to leave for the children's sake. I haven't been paid in four months and now I don't even have a home."

Hundreds of families have also moved out of the east of Gaza City in the al Shaaf and al Tuffah suburbs after Israeli tanks took up position on Wednesday. Two tanks were visible on hills above the suburbs and many more could be heard shooting and moving in the narrow streets.

Scores of Palestinian fighters armed with rifles attempted to approach the tanks, which - supported by drones and helicopters - fired shells and machine guns throughout yesterday. At Shifa Hospital, the ambulances lined up to deliver the injured and crowds of men waited to take away the dead.

Dr Jumah Sakkah said the hospital had taken in 16 injured people and two had died. The death toll later rose to four. He said that all of the injured were non-combatants.