Thousands of Hamas supporters have turned out for the funeral of Adnan al-Ghoul, one of the movement's leading figures in the Gaza Strip.
Crowds flocked to the funeral in the streets of Gaza City
Hamas has vowed revenge after he was killed in an Israeli air attack on his car in Gaza City on Thursday night.
"Our reply will be very severe and we will continue our resistance," Hamas leader Ismail Haniya told crowds.
Loudspeakers led the chanting as thousands of Hamas supporters filed down one of Gaza City's main avenues.
Mr Ghoul is the latest in a long line of the movement's leaders to have been killed in Israeli air strikes.
Almost the entire echelon of men who founded the movement in the late 1980s has now been wiped out.
An engineer and alleged bomb maker, Mr Ghoul was described by Israel as "the father of the Qassam rocket" - a rocket Gaza militants have fired frequently into Israel.
Stopping such rockets was the stated aim of a recent massive Israeli operation in northern Gaza.
Adnan al-Ghoul's son and daughter mourn their father's death
According to B'tselem, an Israeli human rights group, more than 175 members of Palestinian militant groups have been the victims of what Israeli officials call "targeted killings" since September 2000.
At least 100 Palestinian bystanders have been killed in the course of the killings, the group says.
In southern Gaza, Israeli tanks and bulldozers moved about 100 meters into the Rafah refugee camp, witnesses said. Palestinian gunmen are reported to have returned fire.
Nearby, in the buffer zone along the Egyptian border, an Israeli soldier was killed in an explosion on Thursday.
The funeral procession was headed by children waving the movement's huge green banners, followed by a rank of militants and armed men wearing masks, says the BBC's Alan Johnston in Gaza.
Behind them marched the great throng of mourners.
On their shoulders they carried Adnan al-Ghoul's coffin, wrapped in a Hamas flag.
Adnan al-Ghoul was one of the top men in Hamas's military wing.
The killing of Mr Ghoul comes just a few days before the Israeli parliament, the Knesset, votes on Prime Minister Ariel Sharon's proposal to withdraw soldiers and settlers from the Gaza Strip.
The BBC's James Reynolds in Jerusalem says Mr Sharon has made it clear he wants to destroy Hamas before leaving Gaza.
Israel has occupied Gaza since 1967. Under Mr Sharon's plan, 8,000 settlers and the soldiers that protect them will leave the strip.
Israel will maintain control of Gaza's borders, coastline and airspace, and says it will continue to carry out military operations in Gaza.