Hamas is threatening to harm kidnapped Israeli soldier Gilad Shalit if Israel Defense Forces carry out a planned large-scale operation in the Gaza Strip, Israeli Army Radio reported Friday.

The Saudi newspaper Al-Jarida reports that Hamas' Syrian-based leader Khaled Mashaal also threatened increased violence against Israel.

According to the report, Hamas is threatening to carry out suicide bombings deep inside Israeli territory as well as kidnap additional Israeli troops.

Hamas spokesman Abu Mujahed told Nazareth-based newspaper A-Sinara that if Israel were to invade Gaza, the group would begin rocket attacks on Israeli cities.

The threat came as four Gaza Strip Palestinians were killed in an explosion during the funeral for an Islamic Jihad militant who died in an Israeli air strike, according to local medical officials and the police agency run by Hamas.

The blast wounded 35 others, four critically, according to the emergency chief at Gaza City's Shifa Hospital, Bloomberg News reported.

Hamas, an Islamic group designated a terrorist organization by the United States and the European Union, seized Gaza in June, leaving Palestinian Authority President Mahmoud Abbas in control of the West Bank. While street fighting between Hamas and Abbas' Fatah movement ended with the takeover, they still compete for the loyalty of Palestinians.

An Israel Defense Forces spokeswoman said the air strike followed the firing of a rocket barrage on Israel by Palestinian militants. The homemade Qassam rockets hit a house in the Israeli town of Sderot, injuring a woman, the IDF said.

Islamic Jihad shares Hamas' declared goal of destroying Israel and is responsible for many of the rocket attacks launched at Israel from Gaza. In the past week, Palestinians fired about 25 mortar shells and 30 rockets into Israeli territory adjacent to Gaza, the IDF said in an e-mailed statement.