The Palestinian Islamist movement, Hamas, has said two members of its military wing have been killed in clashes with Israeli forces in Gaza.
The Israeli military has intensified operations in Gaza this week
It said they were killed by air strike as they fought Israeli ground forces in the north of the coastal territory.
A third died of wounds he sustained on Thursday, bringing to 37 the number of Palestinians killed in the last week.
Earlier, the UN secretary general urged both sides to take urgent measures to attempt to end the escalating violence.
Ban Ki-moon appealed to the Palestinians for "an immediate cessation" of sniper and rocket attacks from Gaza into Israel, and for "maximum restraint" on the part of the Israeli military.
He also warned that the Israeli government's decision to close border crossings into Gaza would only worsen the humanitarian situation.
Israel says its military operations, along with the closures, are intended to stop militants firing rockets into its territory.
But Palestinian militants say the rockets are a response to continued Israeli aggression and occupation of the West Bank.
Early on Saturday morning, Israeli forces backed by several tanks and bulldozers entered northern Gaza and searched several homes in the Jabaliya refugee camp.
Members of the military wing of Hamas, the Izzedine al-Qassam Brigades, exchanged fire with the troops. Two militants were later killed when Israeli aircraft fired three missiles at them.
The Hamas-run interior ministry in Gaza was bombed on Friday
An Israeli army spokesman said four other Hamas militants were captured during the raid and that they had been taken into Israel for questioning.
Hamas, which seized control of the Gaza Strip in June, confirmed the arrests and said the men had "fought until the last bullet".
The Israeli incursion came a day after a Palestinian woman was killed and more than 40 people were injured when an Israeli missile struck the vacant Hamas-run interior ministry headquarters in Gaza City.
Meanwhile, a senior Hamas official has accused the rival Palestinian faction, Fatah, of plotting to assassinate the former Palestinian Prime Minister, Ismail Haniya.
Said Siyam, who served as interior minister in Mr Haniya's cabinet, said Hamas security forces had detained a would-be suicide bomber in Gaza who had confessed to planning to blow up Mr Haniya at Friday prayers.
Fatah, which is led by Palestinian Authority President Mahmoud Abbas, dismissed the accusation as ridiculous.