Hamas has warned Israel will be defeated if it attempts a full-scale invasion of the Gaza Strip. More Israeli air strikes overnight killed Abu Zakaria al-Jamal, a senior leader of Hamas's armed wing. But the Islamist group remained defiant as Israeli ground forces massed on the border with the Palestinian territory, fuelling fears of a full-scale invasion. Hamas leader Khaled Meshaal said: "We are ready for the challenge, this battle was imposed on us and we are confident we will achieve victory because we have made our preparations." On Thursday, an Israeli air strike killed another Hamas leader, Nizar Rayyan. Most of Hamas's top officials have gone into hiding, anticipating assassination attempts by Israel. A week after Israel launched devastating air strikes against the Palestinian enclave with the declared aim of ending Hamas rocket attacks on its southern towns, an end to hostilities remains elusive despite international diplomatic efforts. Gaza medical officials put the Palestinian casualty toll at at least 431 dead and 2,000 wounded and a United Nations agency said more than a quarter of those killed were civilians. A leading Palestinian human rights group put the figure at 40 percent. One missile killed three Palestinian children aged between eight and 12 as they played on a street near the town of Khan Yunis in the south of the strip. One was decapitated. Four Israelis have been killed by Palestinian rockets, including longer-range weapons that have hit the port of Ashdod and the desert town of Beersheba. The United States has demanded Hamas, which Israel says has been smuggling weapons through tunnels under Gaza's border with Egypt, take the first step by halting rocket attacks on Israel. President George W Bush said: "Another one-way ceasefire that leads to rocket attacks on Israel is not acceptable." Tens of thousands of protesters will voice their anger at the Israeli bombardment later in a series of rallies across the UK. Up to 20,000 people - including the singer Annie Lennox, Respect MP George Galloway and ex-Mayor of London Ken Livingstone - are expected to march along the Embankment in London before walking to Trafalgar Square to call for an end to the Israeli attacks.