Hamas militants in the Gaza Strip fired more than 35 rockets towards Israel today, the army and the Islamist group said, hours after the Israeli army killed six militants in the coastal territory.
An Israeli police spokesman said the rockets landed in southern Israel, causing no damage or injuries.
Hamas claimed responsibility for the attacks, the first such announcement by the Islamist group since an Egyptian-brokered ceasefire with Israel went into effect on June 19.
Palestinian officials said they had been informed by Israel that all commercial border crossings with the Gaza Strip would remain closed on Wednesday in response to the rocket attacks.
Israeli airstrikes killed five militants and Israeli soldiers shot dead a gunman during an incursion into the Gaza Strip on Tuesday.
The army said it launched the airstrikes after militants attacked soldiers who entered the Gaza Strip to destroy a tunnel that Hamas had planned to use to kidnap Israeli soldiers.
The latest violence could jeopardise Egyptian efforts to extend the fragile ceasefire in the Gaza Strip and further complicate Cairo's efforts to secure the release of an Israeli soldier kidnapped by Hamas two years ago.
Hamas has said it would release soldier Gilad Shalit in return for hundreds of Palestinians held by Israel for their involvement in violent attacks against Israeli civilians during a Palestinian uprising.
Israel has agreed in principle to a prisoner exchange deal with Hamas but Israeli officials have had reservations about the idea of releasing prisoners "with blood on their hands."
Also at stake are efforts by the Arab world to reconcile the Palestinian Fatah and Hamas factions during a summit in Cairo next week.
Relations between the two rivals soured two years ago when Hamas won a parliamentary election. A year later, Hamas seized control of the Gaza Strip from Fatah forces loyal to President Mahmoud Abbas who holds sway in the Israeli-occupied West Bank.
Hamas opposes Abbas's peace talks with Israel that Washington launched a summit in Annapolis, Maryland, last year with the hope of shepherding the two sides towards a deal before President George W. Bush leaves office in January.
US Secretary of State Condoleezza Rice arrives in the region on Thursday in a bid to salvage the peace process that has so far shown little signs of a breakthrough.
President elect Barack Obama has said resolving the Israeli-Palestinian conflict would be a top priority for his administration.