Gaza militants fired rockets Tuesday after the death in Israeli custody of a leading Palestinian figure in the Islamic Jihad group, who had been on hunger strike for nearly three months.
The cross-border fire followed the death of Khader Adnan, who had been on hunger strike since his detention by Israeli forces in the occupied West Bank in February.
Israel's prison service announced the death of a detainee affiliated to Islamic Jihad, who was "found early this morning in his cell unconscious".
The news was swiftly followed by rocket fire towards Israel, an AFP journalist witnessed, with the Israeli military reporting three rockets "fell in open areas".
Adnan's death was described as a "deliberate assassination" by Palestinian prime minister Mohammad Shtayyeh.
"By rejecting his request for his release, neglecting him medically and keeping him in his cell, despite the seriousness of his health condition," the premier said in a statement.
Adnan, 45, was the first Palestinian to die as a direct result of a hunger strike, according to the Palestinian Prisoners' Club.
Other Palestinian detainees have died "as a result of attempts to force feed them", the advocacy group's director, Qaddura Faris, said.
A senior Israeli official described Adnan as "a hunger striker who refused medical attention, risking his life".
"In recent days, the military appeal court decided against releasing him from detention solely on the merit of his medical condition," said the official, who requested anonymity.
Adnan was described by the official as an "operative" with Islamic Jihad, who was facing charges related to his activities within the militant group.
- Prisoner's farewell message -
Islamic Jihad, which is considered a terrorist organisation by the European Union and the United States, warned Israel will "pay the price for this crime".
"The free hero, Khader Adnan, died as a martyr in a crime committed by the enemy in front of the world," the militant group said in a statement.
Israel's prison service said Adnan was in jail for the 10th time and his wife, Randa Mousa, previously told AFP her husband had carried out multiple hunger strikes in detention.
"(He is) refusing any support, refusing medical examinations, he is in a cell with very difficult detention conditions," she told AFP last week.
Israel has occupied the West Bank since the Six-Day War of 1967 and its forces regularly detain Palestinians, who are subject to Israeli military courts.
In his final message, Adnan said he was "sending you these words as my flesh and fat has melted."
"I pray that God accept me as a faithful martyr," he wrote, in a message published Monday by the Palestinian Prisoners' Club.
A medic from the group Physicians for Human Rights Israel visited Adnan in prison earlier this week and warned that he "faces imminent death", while calling for him to be "urgently transferred to a hospital."
Israeli authorities had refused to move Adnan to hospital, according to the rights group and his wife.