Witnesses say Israeli helicopters fired missiles into Gaza shortly after Palestinian militants killed five Israelis at a busy crossing between Israel and the Gaza Strip.

The witnesses say two Israeli missiles hit the Deir al Balah refugee camp.  They say the target was a building belonging to a charity linked to a militant group.

An hour earlier, Hamas, al-Aqsa Martyrs Brigades and the Popular Resistance Committee carried out the attack at the Karni crossing.  Three Palestinians were killed in the bomb attack.

The upsurge in violence comes as newly-elected Palestinian President Mahmoud Abbas again called for attacks on Israelis to stop.  Israeli Prime Minister Ariel Sharon, who is expected to meet with Mr. Abbas within days, insists peace negotiations can not be revived unless Palestinians crack down on militants.

Some information for this story provided by AP and AFP.