"This is the right of Palestine; it has the right to defend itself, and there were nine martyrs in one day and violations that must be responded to," Meshaal told reporters after talks with Amr Moussa, the Arab League's secretary-general, in Cairo.
An Israeli military spokeswoman confirmed Saturday's shooting and said the three men were killed while trying to place explosive devices.
Izz al-Din al-Qassam Brigades, the military wing of the Hamas, confirmed that the three killed Palestinians and the injured fourth belong to the group.
End of ceasefire
The brigades resumed firing rockets into Israel on Tuesday after the killing of nine Palestinians in raids last week, which it cited as ending the five-month ceasefire.
Other Palestinian factions, including the National Resistance Committees, al-Nasir Salah al-Din Brigades and Palestine's Mujahidin Brigades, have issued statements claiming responsibility for firing a number of rockets at Israeli targets north and east of Gaza Strip, Hiba Akila, Al Jazeera correspondent, said.
The factions have vowed to continue firing rockets at Israeli targets in response to aggressive Israeli practices in the Gaza Strip and continuing military operations and arrest campaigns in the West Bank, Akila said.
However, Palestinian leaders said the future of the cease-fire depended on Israeli actions.
Ehud Olmert, the Israeli prime minister, decided in talks with security chiefs on Wednesday to step up "targeted attacks" against Palestinian rocket-launching crews.
Ismail Haniya, the Palestinian prime minister, said his government would reassess its strategy in one to two months if international sanctions against the Palestinian were not lifted.
Haniya leads a unity government with Mahmoud Abbas, the Palestinian president.