GAZA CITY (AFP) - Israel and the Islamist Hamas movement traded threats on Thursday, a day fierce fighting in the Gaza Strip killed 18 Palestinians, including a cameraman for an international news agency. Hamas vowed to avenge Wednesday's Israeli assault on the impoverished territory, but Israeli Prime Minister Ehud Olmert said the Islamist movement bears "direct responsibility" for the fighting, which killed three Israeli soldiers. "We consider that Hamas bears sole, direct responsibility for what happened in Gaza and it will pay the price," Olmert said in an interview with Israel's Maariv newspaper. Israel has repeatedly threatened to launch a wide-scale operation to oust Hamas from Gaza, but the media has speculated that it may wait until after the week-long Jewish Passover holiday, which begins on Saturday (tomorrow). Reacting to Wednesday's violence, which also saw the deaths of five Palestinians under the age of 15, Hamas spokesman Fawzi Barhum told AFP that "all options are open to repel this aggression against our people." In an Internet statement Hamas called on its fighters to attack Israel "in every place and with all means available." Israel troops continued to strike Palestinians on Thursday. They killed two Islamic Jihad fighters during a predawn arrest operation in the West Bank and another in southern Gaza who the army said approached a border crossing. Witnesses said a dozen Israeli military vehicles advanced into the area near the Kerem Shalom crossing and that there was a heavy exchange of fire nearby at Gaza's abandoned and mostly demolished airport. Hundreds of people marched in Gaza City at the funeral for 23-year-old Reuters cameraman Fadel Shana, who was killed by a shell fired from an Israeli tank he was filming during Wednesday's incursion. According to Dr Muawiya Hassanein, the head of Gaza emergency services, most of the Palestinians killed on Wednesday were civilians. In Al-Bureij on Thursday the family members of those killed gathered at outdoor funeral tents to mourn their loved ones. "May God destroy the Jews. They broke my heart, they tore it out of my chest." said Um Talha, whose 13-year-old son was killed in the air strike. "He was my youngest son. I hope he will go to paradise and they will go to hell," she said. Palestinian President Mahmud Abbas, on a visit to Moscow, on Thursday called for a new Middle East peace conference in Moscow "as soon as possible," saying this was needed to spur talks with Israel that were moving too slowly. "We want the Moscow conference to be held as soon as possible and we hope that it will succeed in pushing the peace process forward," Abbas said in a lecture to Moscow university students. He said a new impetus was needed to follow on from a conference last November hosted by US President George W. Bush in Annapolis, in the United States.