Israel has launched two air strikes in the Gaza Strip against militants from the Palestinian Hamas movement.
Tensions have escalated in the past few days
Hamas said two people were killed in the first strike near Beit Lahiya.
Later on Sunday residents of Gaza City say the Israeli air force carried out another attack, destroying a car and slightly injuring its driver.
Israel said it targeted militants on their way to launch rockets at Israel. Hamas said it fired several rockets, one of which badly injured an Israeli.
Hamas said it was retaliating for the deaths of seven people on a Gaza beach, apparently killed by Israeli shelling.
The rockets were the first it had fired since its truce 16 months ago, it said.
Later in the day a Palestinian from East Jerusalem was shot dead on a road linking Jerusalem with the West Bank. The motive of the killing was not clear.
And in further signs of tension between Palestinian factions, two key militants have withdrawn their support for a peace plan which implicitly recognises Israel.
Hamas's Abdul Khaleq Natsha and Bassam al-Sadi of Islamic Jihad - both prisoners in Israeli jails - accused Palestinian leader Mahmoud Abbas of seeking to exploit it for political gain.
Mr Abbas has endorsed the plan, which was drawn up by a group of Hamas and Fatah prisoners and urges the establishment of a Palestinian state on land occupied by Israel in 1967.
He has demanded that the Hamas-led government accept it, or face a referendum on the issue.
Hamas has repeatedly refused to recognise Israel, and has said a referendum would be illegal.
Hamas said two of its fighters were killed on Sunday in the Israeli strike near Beit Lahiya.
But reports say occupants of the second car to be targeted, in Gaza City, managed to escape
A member of the Palestinian militant group Islamic Jihad was killed in a separate incident in the northern Gaza town of Jabaliya.
There are conflicting reports of how he died. One says he was killed in an Israeli air strike, another says he was killed by an explosion in his home unrelated to any attack.
Israeli Prime Minister Ehud Olmert has expressed regret over the deaths of the seven members of a Palestinian family killed on Friday.
"We regret the death of innocent civilians," he told ministers at the start of his weekly cabinet meeting, AFP reported.
His government has ordered the military to conduct an inquiry into the deaths.
There were emotional scenes in Beit Lahiya on Saturday as thousands of people attended the funeral of the victims - a couple and five of their children.
The killings have sparked fresh criticism of Israel, with Jordan saying they were a crime which would further increase tensions and Turkey calling them a severe blow to efforts to bring peace.
Five Israeli human rights organisations demanded an urgent end to the killing of Palestinian civilians by Israeli security forces.
Mr Olmert will arrive in the UK on Sunday, ahead of talks with Prime Minister Tony Blair on Monday.