The Israeli air force has launched an air strike on militant targets in Khan Yunis in the southern Gaza Strip.
It is the latest in a series of air strikes on Gaza in response to Palestinian rocket attacks into Israel.
In Gaza City, at least four suspected Palestinian militants were killed when two cars in which they were travelling were attacked by Israeli planes.
The Israeli raids, which began overnight, are the first since Israel's military withdrawal from the Gaza Strip.
Israeli officials say large numbers of ground troops have been deployed to the border with Gaza.
Earlier, Israel's Defence Minister Shaul Mofaz threatened to issue a 'crushing response' after Palestinian militants fired more than 20 rockets from Gaza into the city of Sderot.
This morning, Palestinian witnesses said Israeli F-16 warplanes roared over the Gaza Strip, causing sonic booms.
