The Palestinian militant group Hamas has given some of the responsibilities of its assassinated spiritual leader to another of its senior officials.
Hamas says Yassin will not be replaced
Hamas spokesman Abdel Aziz al-Rantissi is taking charge in the Gaza Strip, where Sheikh Ahmed Yassin was based.
"We will fight them (Israelis) everywhere," Mr Rantissi told thousands of Hamas supporters in Gaza.
Mr Rantissi said the militant group would continue to have a separate leadership in the West Bank.
He told the BBC that no-one would replace Sheikh Yassin as a spiritual leader, and that Khaled Meshaal - Hamas' politburo chief living in exile - was the group's overall leader.
'Teach Israel lessons'
"We will hit them everywhere. We will chase them everywhere," Mr Rantissi pledged before Hamas leaders and thousands of mourners who gathered at Gaza's main football stadium to pay their last respects to Sheikh Yassin.
"We will teach them lessons in confrontation," Mr Rantissi said.
He said that Israeli's Prime Minister Ariel Sharon - who personally directed the missile attack on Sheikh Yassin - "will not know security".
"We will fight them (Israelis) until the liberation of Palestine, the whole of Palestine," Mr Rantissi said.
In response, Hamas supporters chanted: "We will sacrifice our blood and souls for you".
Mr Rantissi is one of the founding members of Hamas, and he is a Hamas man through and through, the BBC's Matthew Price in Gaza says.
A medical doctor who had served as Hamas' chief spokesman, Mr Rantissi s considered a hardliner within the group.
He reacted to Sheikh Yassin's assassination on Monday by saying that Israel had "opened the gates of hell".
As he sees it, Hamas must end the occupation of Palestinian lands, in which he includes modern-day Israel, our correspondent says.