Thousands mourn Hamas founder
Angry Palestinians vow revenge after Israeli attack
Mourners hold aloft a coffin during the funeral Monday of those killed in the Israeli airstrike.
CNN's Paula Hancocks reports on the killing of Hamas leader Sheikh Ahmed Yassin.
Israel closes down Gaza City
Israeli spokesman Avi Pazner: 'Terrorist' Yassin deserved to be killed.
EU condemns Israeli attack
GAZA CITY (CNN) -- Tens of thousands of mourners jammed the streets of Gaza City on Monday in a funeral procession for Hamas founder Sheikh Ahmed Yassin, who was killed earlier in the day in a targeted Israeli attack.
Missiles fired from an Israeli helicopter killed Yassin and seven others leaving a mosque.
The strike wounded 16 others, including two of Yassin's sons, hospital sources said.
Mourners waved Palestinian flags and the flags of various Palestinian groups, including Hamas and the Democratic Front for the Liberation of Palestine, as they vowed revenge on Israel.
As Hamas gunmen fired weapons into the air, thousands of Yassin supporters chanted "Hamas is not dead."
Mourners packed the streets and roofs around Yassin's funeral procession as his flag-draped body was carried to a cemetery known as the "martyrs' graveyard." The Palestinian Authority declared three days of mourning.
Sporadic gunfire could be heard late into the night as small groups of Palestinians fired into the air. Verses from the Koran blared from minarets, and Hamas vowed to "shake Israel like an earthquake."
The Israel Defense Forces issued a statement after the strike.
"This morning, in a security forces operation in the northern Gaza Strip, the IDF targeted a car carrying the head of the Hamas terror organization, Sheikh Ahmed Yassin, and his aides," the IDF statement said.
"Yassin, responsible for numerous murderous terror attacks, resulting in the deaths of many civilians, both Israeli and foreign, was killed in the attack."
Palestinian officials condemned Israel's killing of Yassin, calling it an "assassination."
Moves at United Nations
In New York, the U.N. Security Council held private meetings Monday on a grievance filed by the Palestinian Authority.
Palestinians at the United Nations said they want the council to issue a statement that condemns the killing, calls it an execution, and criticizes the violence and damage done to the Middle East peace process.
But Israeli Prime Minister Ariel Sharon thanked the security forces who carried out the operation and said the "war on terror is not over."
"The ideological essence of this man was one -- the murder and killing of Jews wherever they are and the destruction of the state of Israel," Sharon said.
Britain's foreign minister called the attack "unlawful" and condemned it, as did other world leaders. (International reaction)
The U.S. State Department has labeled Hamas, a Palestinian Islamic fundamentalist organization, a terrorist group. Izzedine al Qassam, the military wing of Hamas, which has claimed responsibility for terrorist attacks against Israel's civilians and military, threatened reprisals in a statement.
"Murderous Zionists, you have bestowed martyrdom upon our Sheikh, and we will bestow violent death upon you on every city and every street," it said in a written statement. "The Zionists will soon see, not hear, our response, God willing."
The Izzedine al Qassam statement alleged that Israel would have gotten approval from the Bush administration before striking Yassin, but White House national security adviser Condoleezza Rice, in television interviews, said the United States did not know about the attack in advance.
Meanwhile, the Lebanese militant group Hezbollah named a brigade after Yassin on Monday and sent it to attack Israeli military outposts on the Lebanese border, a Hezbollah spokesman said.
The Israeli military confirmed that Hezbollah had attacked outposts, but reported no damage or casualties.
Weeks of operations in Gaza
Immediately after the attack, the IDF sealed off Palestinian territories in Gaza and the West Bank. Several incidents of violence were reported throughout the region, including a Palestinian stabbing two civilians, the killing of a Palestinian in a village north of Hebron and a Palestinian attacking Israelis with an ax, authorities reported.
The Israeli attack on Yassin followed weeks of Israeli antiterrorist military operations into Gaza. Several Palestinians, including civilians, have died in the operations.
Israel began the counterterror raids after a terrorist bus bombing killed eight people February 22 in Jerusalem.
Al Aqsa Martyrs Brigades, a nationalist militant offshoot of Palestinian leader Yasser Arafat's Fatah movement, claimed responsibility for the bus bombing. Israel and the U.S. State Department consider Al Aqsa Martyrs Brigades a terrorist organization.
Last week, twin suicide bombings jointly claimed by Hamas and Al Aqsa Martyrs Brigades killed 10 people and derailed scheduled talks between Sharon and Palestinian Prime Minister Ahmed Qorei on the so-called "road map" to Mideast peace.
The "road map," backed by the United States, European Union, United Nations and Russia, calls for steps by both sides aimed at ending the conflict and establishing an independent Palestinian state by 2005.
CNN's Talal Aburahma, Chris Burns and Richard Roth contributed to this report.