Israeli air strikes on the Gaza Strip killed 6 people in a violation of truce between Hamas and Israel.
An Israeli army spokeswoman confirmed the air strikes.
The air strike was the first Israeli military attack since the start of a ceasefire was declared on June 19 and which has largely held between Israel and Hamas.
Hamas spokesman Sami Abu Zuhri said the raid proved that Israel was not interested in continuing the ceasefire although he stopped short of saying that Hamas would abandon it.
"The aggression is a major violation of the agreement. If such raids are repeated, fighting will not be limited only to the area east of the central Gaza Strip," Abu Zuhri said.
A statement from Hamas's armed wing said "the current calm agreement will not prevent us from defending our people against Zionist (Israeli) arrogance." It warned of a harsh response.
Response
Hours after the killings, Palestinian fighters in the Strip fired more than 35 rockets towards Israel on Wednesday, Hamas said.
An Israeli police spokesman said they landed in southern Israel, causing no damage or injuries.
Palestinian officials said they had been informed by Israel that all commercial border crossings with the Gaza Strip would remain closed on Wednesday.
PHOTO CAPTION
A wounded Palestinian is carried to a hospital in Gaza October 4, 2008
Agencies