Israeli officials say suspected Palestinian militants in the Gaza Strip have fired 20 rockets Wednesday into southern Israel.
There was no immediate report of casualties.
On Tuesday, the Israeli army said it killed at least six Palestinian militants, in the first armed clash since a June cease-fire in the Gaza Strip.
Military officials said they launched air strikes against militants who were firing mortars at Israeli forces on Tuesday. At least five militants were killed.
Shortly before the air strikes, a Hamas militant was killed in a gunbattle with Israeli troops, who were moving into central Gaza near the al-Bureij refugee camp to destroy a suspected militant tunnel about 250 meters inside the occupied territory.
Hamas issued a statement saying Israel had violated the cease-fire and vowing a harsh response.
The Israeli military claims the move did not violate a truce, but instead was a legitimate step to remove an immediate threat to Israel.
Israel and Palestinian militant groups agreed to a cease-fire that calls for Gaza militants to stop attacks on southern Israel and for Israel to stop military raids and air strikes in Gaza.
Some information for this report was provided by AFP, AP and Reuters.