Israelis descend on Nablus
Israel has begun a pre-dawn military operation in the West Bank town of Nablus.
Palestinian security sources described a mass incursion at 0400 (0200 GMT) with dozens of tanks and armoured vehicles, which took up position around the old city quarter.
The Israeli army confirmed the attack, but gave no further details.
Earlier, Israeli military helicopters fired missiles on Gaza City, targeting a metal workshop which was also attacked in the early hours of Monday morning.
An army spokesman said the workshop was a weapons-making facility.
The operations come a day after Israeli leaders began a military response to a Palestinian attack on a kibbutz on Sunday that killed five Israelis.
Israel says the gunman in the kibbutz attack came from Tulkarm, which was targeted in a raid on Tuesday.
But he allegedly received his orders from the al-Aqsa Martyrs' Brigade, an offshoot of Palestinian leader Yasser Arafat's Fatah movement in Nablus.