Hamas leader Mohammed Deif said the start of Operation Al-Aqsa Storm was in connection to the Al-Aqsa mosque compound in Jerusalem, the third holiest site in Islam.
The site is also located on the holiest site for Jews, who refer to it as the Temple Mount. It has long been a flashpoint between Israelis and Palestinians, with Israeli security services routinely raiding the compound.
Deif said in a recorded message that "enough is enough" and called on Palestinians from east Jerusalem to northern Israel to join the fight. He said that "today the people are regaining their revolution."
Hamas has launched thousands of rockets into Israel in recent days. The Israeli military has responded with airstrikes on Gaza.
At least 40 Israelis and hundreds of Palestinians have been killed in the violence.
The international community has called for a ceasefire, but both sides have so far refused to stop fighting.
The conflict between Israel and Gaza is a complex and long-standing one. The recent attack by Hamas is only the latest escalation in violence. It is unclear what will happen next, but it is clear that the situation is dire.