The first shells landed in the vicinity of Israel's southern Negev region near the Karni checkpoint early on Tuesday. A few hours later, rockets hit the city of Sderot and an open area in western Negev.
As a result, the Israeli military decided to cancel the scheduled opening of all but one of its Gaza border crossings due to security concerns, putting an end to supplies of food and other essential items.
"All crossings except for the Erez checkpoint, which is used for private individuals, are closed on the orders of the Defense Minister," the spokeswoman said.
The Islamic Jihad movement has claimed responsible for the rocket attack on southern Israel, saying it was a response to the killing of one of its commanders and another militant by IDF troops in the city of Nablus in the West Bank, which is not covered by the truce. The IDF only confirmed the death of the Palestinian commander, who they said was planning an attack on Israel.
Hamas, the radical Islamic group which has controlled the Gaza Strip since last June, said they were in favor of maintaining the truce but would not use force against militants firing rockets at Israel.
"Hamas will not become a policeman protecting the enemy's borders," top Hamas leader Khalil al-Hayya told a press-conference in Gaza on Wednesday.
The six-month truce between Israel and Hamas-led militants came into force at 06:00 a.m. local time (03:00 GMT) on June 19. The deal is limited to the Gaza Strip.
Under the agreement, which is now looking increasingly under threat, Israel is to gradually abolish economic sanctions imposed on Gaza, and the sides are to continue to negotiate the release of the kidnapped Israeli soldier Gilad Shalit, who has been held captive in Gaza for exactly two years.
Israeli Prime Minister Ehud Olmert last week described the ceasefire as "fragile" and said he expected it to be "very short."
