Israel Defense Forces troops on Tuesday killed at least 19 Palestinians, including three civilians, in ground and air operations on the Gaza Strip.

On Tuesday evening, an IDF strike targeting a group of militants firing rockets into southern Israel killed two militants in the northern Gaza Strip town of Beit Hanun.

At least 17 Palestinains were killed earlier on Tuesday in raids on Gaza City. Of those, at least 14 were members of armed groups, and 13 of them were Hamas militants. One of the other fatalities was a 65-year-old man, Palestinians said.

The exiled leader of Hamas said Tuesday that the Gaza raids were the fruit of U.S. President George W. Bush's visit to the Middle East region.

Khaled Meshal, in an interview with The Associated Press in Damascus where he lives, accused Bush of inciting Israeli leaders.

"This crime is the ugly fruit of Bush's visit to the region. He has incited the Zionists and has exerted pressure on the Palestinian side to become more hardline against Palestinian dialogue," he said during the interview in his office.

"This proves that our people are great and our leaders sacrifice their sons. These are the real leaders that meld with their people and defend them, not those who infiltrate to the futile negotiating table with the Zionist entity, he said of Fatah."

Mashaal said Hamas will retaliate to the Gaza raid with more resistance, steadfastness and national unity.

"We will not offer more concessions because of these crimes," he added.

Palestinian President Mahmoud Abbas denounced the raids as "a massacre" which would not be forgotten by the Palestinians.

"There was a massacre today against our people, and we say to the world that our people will not remain silent against such crimes," he said.

In a statement, the West Bank-based Palestinian government said Israel's "ugly crimes were a slap in the face" to efforts by Bush and the international community to resume peacemaking that would lead to the creation of a Palestinian state.

President Shimon Peres said as long as Gaza militants continue to fire rockets into the Jewish state, "we are left without a choice but to answer and stop it."

David baker, an official in the Prime Minister's Office, said of the attacks, "These measures will continue until these attacks cease and as to enable our citizens to live in peace in quiet and not to fall victim to incessant Palestinian terror."

One of the 17 killed in the Gaza City raids was the son of Hamas leader Mahmoud Zahar, the last surviving founder of the Islamist group.

The fighting began late on Monday when IDF soldiers backed by tanks and helicopters entered the eastern Gaza City neighborhoods of Sejaiyeh and Zaitoun, trading fire with gunmen.

On Tuesday morning, a Palestinian sniper fired from the border area into Israel, killing a 21-year-old volunteer from Quito, Ecuador, who was working in a field near the kibbutz border fence, Ein Hashlosha's security chief said.

Clashes continued in Gaza through Tuesday afternoon.The violence demonstrated an appreciable escalation of fighting surrounding the Gaza Strip, where daily Qassam rocket attacks have been countered largely by Israeli air strikes against rocket crews and commanders of armed groups.

Some 45 Palestinians were wounded in the fighting, among them an 8-year-old boy who was seriously hurt, medical officials said.

Dr. Moaiya Hassanain of the Gaza Health Ministry said many of the dead and wounded lost limbs.

Because of the high number of casualties, Hassanain questioned whether IDF troops were using tank-fired flechette shells, an anti-personnel weapon that throws out thousands of metal darts

The IDF had no immediate comment on whether such munitions were used.

Shifa Hospital put out a radio call for blood donations because of the large number of wounded.

Hamas called for a general strike in Gaza and the West Bank on Wednesday to protest the heavy number of deaths.

Zahar's son killed while taking part in fighting Mahmoud Zahar, who was serving as Palestinian Authority Foreign Minister when the Hamas-Fatah coalition government collapsed in chaos last year, is seen as one of the more militant leaders of the Hamas political wing.

Hussam Zahar, 24, son of the Hamas leader, was taking part in the fighting when killed, residents said. He was Zahar's second son to die in Israeli-Palestinian violence.

In a 2003 assassination attempt, an Israel Air Force aircraft attacked Zahar's house, wounding him, and killing his elder son Khaled and a bodyguard.

Deputy Defense Minister Matan Vilnai told Army Radio that the younger Zahar, who is survived by a brother and four sisters, wasn't targeted by IDF forces.

As he viewed the body of his son in a Gaza hospital on Tuesday, Mahmoud Zahar accused Bush of prompting further violence on the Palestinians. "This is one of the results of the Bush visit. He encouraged the Israelis to kill our people," said Zahar.

Zahar said his son's death was God's will. "We will respond to them in the appropriate way," he said of the IDF incursion. "We will defend ourselves by all means."

"What is going on in Gaza today is a shame for all of those who cooperated with [U.S. President George] Bush, the criminal, and with the Zionists," Zahar said. "I am talking about all kings, presidents and ministers," he said, in an apparent reference to Arab leaders meeting with Bush.

"We are telling them, today they are killing our sons, tomorrow they are going to kill yours."

Zahar also appeared to blame Abbas, widely known as Abu Mazen, for the IDF incursion and indirectly for his son's death. "This is the hope of Abu Mazen and his colleagues, the collaborators with Israel and the spies of America," Zahar said.

Tanks, bulldozers and copters move in Late on Monday night, an initial IDF unit moved into the Zeitoun area, striking a house used by Palestinian militants to launch projectiles, Hamas security said.

Palestinian gunmen discovered the soldiers, fired at them and an exchange of fire broke out, Hamas said.

IDF tanks, bulldozers and helicopters then entered the area, firing at the militants, Hamas said. Residents of Zeitoun, a Hamas stronghold, said about 10 tanks and armored vehicles had moved into the area by Tuesday morning.

An IDF spokeswoman said the troops were involved in action against "terror infrastructure" in the northern Gaza Strip and that a number of the armed men had been shot.