Hamas names interim leader in Gaza
Militant group spokesman takes over role of slain Yassin
Israel closes down Gaza City
Israel on high alert for reprisals
Israeli spokesman Avi Pazner: 'Terrorist' Yassin deserved to be killed.
EU condemns Israeli attack
GAZA CITY (CNN) -- Abdel Aziz Rantisi was named acting Gaza leader of Hamas until a new leader is chosen, Hamas officials said Tuesday.
Rantisi takes over as details of a letter said to be from Hamas founder Sheikh Ahmed Yassin -- who was killed Monday in an Israeli targeted helicopter attack -- were made public.
A pediatrician by training, Rantisi is a longtime militant. He has been jailed in Israel and by the Palestinian Authority. Israel tried to kill him in June.
Rantisi speaks fluent English and has represented the Islamic fundamentalist organization before the international media.
Israel's security forces were on high alert Tuesday in preparation for reprisals over Yassin's killing. Hamas has vowed to avenge his death.
A member of Hamas was shot and killed by Israeli forces late in the day as he planted a bomb in the Jewish settlement of Morag in southern Gaza, Palestinian sources said.
Hours earlier, Israeli tanks and 25 armored personnel carriers moved into a Palestinian refugee camp near Khan Yunis to bulldoze agricultural land, Palestinian security sources said
And the Israeli air force launched a raid in southern Lebanon that killed two Palestinians, Lebanese sources told CNN. They added the group was a unit of the Popular Front for the Liberation of Palestine (PFLP).
The Israeli air force said several Palestinians were preparing to fire rockets into northern Israel.
Hamas has vowed to retaliate for the killing of its spiritual leader Yassin, who was fired on as he left a mosque.
Tens of thousands turned out Monday for the funeral procession of Yassin, whose flag-draped body was carried through the streets to a cemetery known as the "martyrs' graveyard." (Full story)
Yassin, who founded Hamas in 1987, was one of the most visible symbols of the resistance against Israel. (Key facts)
Seven others were killed with Yassin, who used a wheelchair, and 16 more were wounded, according to hospital sources.
The Palestinian Authority declared three days of mourning Monday and condemned the killing.
The international community roundly condemned the killing, although Israel's most important ally, the United States -- which regards Hamas as a terrorist organization -- criticized the move as a hindrance to peace but stopped short of condemning it. (International reaction)
A letter to this month's Arab League summit, said to be from Yassin and published Tuesday on the Web site for the Palestinian Media Center, urges the Arab world to back the fight against Israel economically and militarily. It read in part:
"Palestine is a Muslim and Arab land. The Zionist Jews stole it from us by the power of arms, and we will get it back only by the power of arms.
"It is a sacred Islamic land. We shouldn't give up one inch of Palestine even though we don't have at this time the needed power to liberate it."
The message read: "Describing our jihad as terrorism by the enemies of God is a great injustice. We hope that the summit will have a clear and non-negotiable position in support of our people.
"Our people need economic support to strengthen their resistance after the evil Jews have destroyed their livelihood and stole their riches. Our people also need military support, as well as security, media, moral, diplomatic support, to help them continue their jihad and we look to the summit to achieve all that, god willing."
CNN translated the letter, which carried the Hamas letterhead, from Arabic to English.