Palestinian resistance group Hamas has threatened to avenge a deadly weekend raid in the movement's Gaza stronghold with attacks inside Israel. In comments on Monday, the Islamic group's leader in Gaza, Mahmud al-Zahar, also poured cold water on calls for a ceasefire with Israel. "Aggression from Israel will be reacted by self-defence ... whether within the occupied territories or outside the Green Line," al-Zahar said. His comments came after 11 Palestinians were killed over the weekend during an Israeli raid into the Khan Yunus refugee camp in southern Gaza, the deadliest offensive since the death of Palestinian leader Yasir Arafat. Mahmud Abbas, Arafat's successor as Palestinian Liberation Organisation (PLO) chairman, has been trying to persuade Hamas - responsible for most of the anti-Israeli attacks during the course of the four-year intifada - to call a new ceasefire. **Ceasefire calls*** But al-Zahar said that only a complete end to the Israeli occupation of the West Bank and Gaza Strip and a release of all 8000 Palestinian prisoners would lead to such a move. "We have already declared our stand - it should be a bilateral stoppage. Israeli aggression first, the release of all Palestinian detainees, the opening of our borders, real withdrawals from our areas, not redeployment," he said. "The occupation is the cause. The elimination of the occupation will spontaneously stop this aggression." Al-Zahar was speaking on the sidelines of a seminar on the Middle East where delegates appealed for an end to attacks on civilians. Alexander Kalugin, Russia's envoy to the region, said that it would be impossible to put pressure on Israel to tone down its activities as long as attacks against civilians continued. **International pressure*** "We expect the Palestinians to agree on the kind of act that will preclude any terrorist act against Israeli civilians and we hope that Israel will respond positively to any agreement among the Palestinian factions," he said. Al-Zahar welcomed the prospect of international pressure on Israel which, if successful, could lead to a ceasefire from his group. "If the neutral side, the quartet [sponsors of the road map peace plan] or others can convince the Israelis to fulfil our demands, I think we can reach an agreement." Al-Zahar also played down differences with Abbas who described the armed uprising last week as harmful to the Palestinian cause and called for a laying down of weapons. "We understand that in every community there are big differences between all people and factions, and we accept that," he said. "It is not a precondition for Abu Mazin [Abbas] to be Hamas or for Hamas to be PLO, so it is a matter of how to reconciliate and reach a final goal." **PHOTO CAPTION*** Mahmud al-Zahar. (Al-Jazeera)