Three foreign workers were injured in the attack, which came after Israeli tanks shelled Gaza in response to an earlier salvo of rockets.

The prisoner, Khader Adnan, was a senior figure in Islamic Jihad who had been charged with terrorism offences.

Israeli authorities said he refused medical care during his 87-day strike.

But one of his lawyers accused them of medical negligence and the Palestinian prime minister described his death as a "deliberate assassination".

An umbrella group representing militant groups in Gaza, including Islamic Jihad, said the rocket fire was "an initial response to this heinous crime".

The first three rockets, which were launched hours afters after Adnan's death was announced, landed in open areas, the Israel Defense Forces (IDF) said.

Later the IDF said it had hit Gaza with "tank fire" in response. Soon afterwards, the IDF reported that militants had fired another 22 rockets, four of which were intercepted by Israel's Iron Dome missile defence system and 16 landed in open areas.

At least one hit a building site in the southern Israeli city of Sderot, where the Magen David Adom ambulance service said three foreign workers were wounded, one seriously, by shrapnel.

 Palestinian militant groups in Gaza claimed the rocket fire was "an initial response to this heinous crime"

Tensions had flared with the death of Khader Adnan, who had been in and out of detention by Israel over the past two decades.

The 45-year-old had been on hunger strike four times before in protest, helping to make his name well known to Palestinians.

While Palestinian prisoners in Israel jails often take a stand by refusing food, this is believed to have been the first such death in three decades.

Adnan began a fifth hunger strike immediately after being detained by Israeli forces at his home in Arraba, near the city of Jenin in the northern West Bank, on 5 February.

Israeli authorities accused him of supporting terrorism, affiliation with a terrorist group and incitement, and he was due to go on trial this month.

But the Palestinian prisoners' rights group Addameer said he was being held on "spurious charges intended to further suppress Palestinian activists".

Last week, the Palestinian Prisoners' Club, another advocacy group, warned that Adnan's health situation was "very serious". It said he was refusing nutritional supplements and medical examinations.

Adnan's wife, Randa Mousa, said he was doing that because Israeli authorities had "refused to transfer him to a civilian hospital [and] refused to allow his lawyer a visit".

On Tuesday, the Israel Prison Service announced that Adnan was "found early this morning in his cell unconscious", and that was taken to a hospital where he was declared dead after efforts to revive him failed.

A senior Israeli official told AFP news agency that Adnan had risked his life by refusing medical attention, adding: "In recent days, the military appeal court decided against releasing him from detention solely on the merit of his medical condition."

However, Palestinian Authority Prime Minister Mohammed Shtayyeh said Israel had "carried out a deliberate assassination against the prisoner Khader Adnan by rejecting his request for his release, neglecting him medically, and keeping him in his cell despite the seriousness of his health condition."

Islamic Jihad, which is the second most powerful militant group in the Hamas-controlled Gaza Strip, said: "Our fight is continuing and the enemy will realise once again that its crimes will not pass without a response."

 Khader Adnan's widow, Randa Mousa, said she wanted no bloodshed because of his death

Randa Mousa said she did not want people to grieve her husband's death.

"We will only receive well-wishers, because this martyrdom is [like] a wedding, a [moment of] pride for us and a crown on our heads," she told journalists in Arraba, according to AFP.

She also insisted she did not want "a drop of blood to be shed" in retaliation.

"We don't want anyone to respond to the martyrdom. We don't want someone to launch rockets and then [Israel] strikes Gaza," she added.

The fate of their prisoners in Israel is a top issue for Palestinians, who hold Israel responsible for their well-being.

There are some 4,900 Palestinians in Israeli prisons, according to Addameer.

Most are serving sentences after being convicted by Israeli courts or are being held for questioning, have been charged, or are awaiting or standing trial. It says another 1,016 are in "administrative detention", a controversial measure under which suspects are held indefinitely without charge or trial for renewable six-month periods. Palestinians regard all those held by Israel as political prisoners.

Addameer says the deportation of Palestinians from the occupied West Bank to prisons in Israel is illegal under international law. Palestinians also protest that it makes prison visits difficult because of strict conditions on Palestinians entering Israel from the West Bank.

By David Gritten
BBC News