Israeli missiles hit just seconds after the fighters fired off homemade Qassam rockets, Palestinian sources said. The first missile hit two men on an empty wagon cart and killed them instantly.
The second missile hit a nearby group, killing one fighter, witnesses said.
The fighters were from the Popular Resistance Committees, an umbrella group of Palestinian resistance groups fighting Israeli occupation, Palestinian sources said.
Aljazeera's correspondent in Gaza, Samir Abu Shamala, reported that a mute Palestinian civilian was shot in the head and killed by Israeli occupation soldiers in the Jabalya refugee camp on Sunday afternoon.
Earlier, Israeli Prime Minister Ariel Sharon expressed his satisfaction with the ongoing onslaught in the Gaza Strip which has already killed at least 66 Palestinians.
Death toll rises
The five-day Israeli campaign
shows no sign of abating
A Palestinian teenager died of his injuries after being seriously wounded in an Israeli air strike on Jabalya refugee camp in the northern Gaza Strip on Sunday, Palestinian hospital sources said.
Dr Bakr Abu Sufiya, head of the emergency room at Gaza City's Shifa hospital, named the latest victim as 14-year-old Nidal al-Madhun.
Two more Palestinian teenagers died of their injuries after being seriously wounded by Israeli army gunfire in Jabalya, Palestinian medics said.
Their deaths brought to 10 the number of Palestinians killed in escalating violence in the area on Sunday, the fifth straight day of a massive Israeli operation. Six of them were resistance fighters, Palestinian sources said.
Raids to continue
Vowing to continue the series of raids which began on Tuesday, Sharon said: "The operation is progressing in a satisfactory way. Our forces are acting professionally and efficiently. This is not a short operation. We should act for as long as the danger exists."
Ariel Sharon has vowed to
continue the Gaza onslaught
The raids are the largest and deadliest in the Gaza Strip in four years and have seen up to 2000 Israeli occupation troops backed by 200 tanks and helicopters being deployed.
Dozens of Palestinian resistance fighters and citizens, including women and children, have been killed or injured and rows of houses have been bulldozed.
Israel says the offensive, dubbed Days of Penitence, is aimed at halting Palestinian rocket attacks on border towns and settlements in the area.
The onslaught has focused on the northern part of the crowded coastal territory, home to 1.3 million Palestinians.
Troops have seized up to 9km of the Gaza Strip as a "buffer zone" and pushed deep into the teeming Jabalya refugee camp.
Sharon said late on Saturday the occupation forces' mission was to "completely" bring to an end the launching of Qassam rockets by Palestinian resistance fighters.
Israeli troops have cleared a
9-km buffer zone in the area
He told Israel Radio: "This operation will continue as long as necessary."
Early on Sunday, two members of al-Quds Brigades, the military wing of Islamic Jihad, were killed when an Israeli helicopter fired missiles in the Jabalya refugee camp.
According to Aljazeera's correspondent, the men were reported to have been attempting to plant an explosive device.
The correspondent cited other Palestinian sources who said the fighters were killed when an Israeli tank, stationed at the camp's outskirts, fired a shell at a Palestinian citizen's home.
The fighters, who were hiding inside, were killed and the home was damaged.
Also on Sunday, Palestinians found the remains of a man who had been decapitated, apparently by a tank shell. Hospital officials later identified him as a Hamas activist.
Also on Sunday, Israeli tanks and bulldozers opened a new front, moving from a Jewish settlement in southern Gaza into the Khan Yunus refugee camp, residents said.
In the West Bank city of Ram Allah, Prime Minister Ahmad Quraya urged resistance groups "to think about the higher national interest and not give Israel excuses to continue the aggression against our people in Gaza", hinting at a halt to rocket launches.
Palestinian activists have been
targeted in missile strikes
But Palestinian president Yasir Arafat referred to Israel's campaign as a "monstrous, criminal, inhumane attack on our people".
He earlier called on "the entire world to act immediately and rapidly to stop the criminal and racist" attack.
Iran on Sunday joined the chorus of international condemnation accusing Israel of committing genocide in the Gaza Strip and called for international intervention to halt the latest operation, the state news agency IRNA reported.
"The genocide of Palestinians and violations of international laws by the Israelis means that action from the international community is needed to defend the defenceless people of Palestine," foreign ministry spokesman Hamid Reza Asefi was quoted as saying.
"The brutal slaughter of innocent people in the Gaza Strip has further exposed the inhuman nature of Zionist regime's leaders to the public."