Three Palestinians were killed when Israeli troops raided a village in the Gaza Strip early on Friday morning, Palestinian sources have said.
The Israelis reportedly surrounded the home of senior Hamas activist Adnan al-Ghoul, but he was not at home at the time of the search.
Israel has confirmed that an operation was in progress in the area but made no further comment.
We are still waiting for responses from our [fighters] in the field and also from those in Israeli prisons - we cannot do that in a few hours
The raid came as Palestinian groups debate the possibility of a temporary ceasefire amongst themselves.
Palestinian sources said the Gaza raid included more than 10 tanks and two helicopters.
Ghoul's son Mohammed, 24, was then reportedly crushed to death when Israelis demolished the house.
Ghoul's brother Imran was also found dead in the house, the AFP news agency quoted Palestinian sources as saying.
It was not clear if he was crushed in the demolition of the building or shot dead earlier.
A third man, Mohammed Abu al-Taya, was shot during clashes.
He was a member of the al-Aqsa Martyr's Brigades, a militant offshoot of Palestinian leader Yasser Arafat's Fatah movement, Palestinian sources said.
Israel has tried to arrest Mr Ghoul before. His whereabouts are not currently known.
Time to consider
Palestinian militant groups have said they need more time to consider a proposal to suspend attacks on Israelis.
Hamas, al-Aqsa Martyrs' Brigade and Islamic Jihad are said to be close to a deal, which could be a crucial step forward for the international peace initiative known as the roadmap.
Israel says there should be no talks with militants
But their leaders suggested any breakthrough may not come before the weekend - contradicting earlier remarks by Palestinian leader Yasser Arafat that an announcement was expected "within hours".
The BBC's Barbara Plett in Ramallah says any ceasefire will be a unilateral move by the Palestinians as the Israelis continue to insist that militant groups are dismantled, not negotiated with.
Palestinian Prime Minister Mahmoud Abbas - better known as Abu Mazen - has been trying to secure agreement from the armed factions to suspend attacks on Israelis for a period of three months.
But correspondents say Mr Arafat continues to have a vital role to play with the militant groups and with the broader Palestinian public.
His comments, after a meeting with Ireland's foreign minister, were explicit.
Arafat: Still has a role
"Until now, it has not been officially decided, but we expect that in the coming few hours, there will be a declaration," he said.
Mohammad al-Hindi, a top Islamic Jihad official, said truce talks had been ongoing, but Mr Arafat's timetable was too optimistic.
"We are still waiting for responses from our [fighters] in the field and also from those in Israeli prisons. We cannot do that in a few hours," he said.
Asked when a truce announcement might be made, Mr Hindi said: "It is fair to say in the next few days."
Abdel-Aziz al-Rantissi, second-in-command of Hamas and himself a target of a recent Israeli assassination attempt, agreed that it would be days before a final decision was made, the AFP news agency reported.
Correspondents say that details may yet have to be worked out and the success of a cessation of attacks on Israelis is far from guaranteed.
A truce declaration could coincide with Sunday's scheduled visit to the Middle East by US National Security adviser Condoleezza Rice.
She and US Secretary of State Colin Powell have been personally charged by the president to promote the roadmap and do what they can to bring peace between the Israelis and the Palestinians.
Ending violence is a key first stage on the US-backed roadmap peace plan which promises security for Israel and a Palestinian state, but bloodshed continued on Thursday.