An Israeli helicopter has fired a missile in the northern Gaza Strip, injuring three people, witnesses say.
The incident occurred near the town of Beit Hanoun, where Israeli forces have expanded operations against militants firing rockets into southern Israel.
Tanks had moved to the entrance of nearby Jabaliya refugee camp - one of the largest with about 45,000 people.
And the UN agency for Palestinian refugees is evacuating all its non-essential foreign staff from Gaza.
It is the second time that the agency has ordered such a redeployment in recent weeks.
No safe route
An Israeli military source was quoted as telling the AFP news agency that the Israeli Air Force had fired into open fields near Jabaliya.
Last month Israeli tanks and infantry stormed into the area to destroy farmland Israel says was being used as cover by Palestinian militants firing makeshift rockets.
The southern Israeli town of Sderot, some three kilometres (two miles) from the Gaza perimeter fence, has frequently come under fire from such rockets which killed two Israelis in late June.
A spokesman for the UN Relief and Works Agency (Unrwa), Johan Eriksson, said the decision will leave only nine foreign workers in Gaza.
Mr Eriksson said that reports that Israeli forces had moved to the edge of the camp meant there was no longer a safe route between Gaza City and the Erez crossing point into Israel.