A Palestinian infiltrator killed five Israelis in a Jewish settlement in the West Bank early on Saturday, an Israeli military spokeswoman said.
Israeli media said the attacker broke into a house in the settlement of Itamar in the middle of the night and stabbed to death a couple and three children, including a baby, from the same family.
"Five civilians were killed in this terrorist attack," the spokeswoman said.
She said troops were searching for the attacker in the area around Itamar, which is near the Palestinian city of Nablus. She gave no further details.
According to the settlers' YESHA council, about 100 families live in Itamar.
There was a similar attack on the settlement during a Palestinian uprising in 2002, when a gunman broke into a house and opened fire, killing four members of one family and a neighbour.