Israel is warning that fighting in the Gaza Strip could get worse before its mission against Hamas militants is complete. Troops are deep inside the region trying to seize ground from the militants. More than 540 Palestinians have been killed since Israel began its campaign ten days ago. At least 18 are reported to have died in overnight shelling. Many civilians lack food, water and power and hospitals are struggling to cope with the casualties of the conflict. Israeli Defence Minister Ehud Barak says offensive will continue until communities in Israel are safe from Hamas rocket strikes despite international pressure to secure a ceasefire. Save the Children has called for aid to be let in to the stricken area and said that 50,000 children are already suffering from chronic malnutrition. More than 2,000 families were displaced prior to the launch of the ground offensive on Saturday with charities expecting the number to increase significantly as fighting escalates. Politicians led by Prime Minister Gordon Brown have united to urge both sides to reach an immediate ceasefire. Mr Brown said it was vital that the international community, including the Arab League, worked together to find a workable solution to the problem. He said: "This is a very dangerous moment, I think everybody around the world is expressing grave concern. What we've got to do almost immediately is to work harder than we've done for an immediate ceasefire." US President George W Bush has insisted that any ceasefire to end the Gaza crisis must include provisions to prevent Hamas from continuing to use the coastal strip to fire rockets into Israel. Mr Bush made it clear while he is concerned about deteriorating conditions for Palestinians living in Gaza that he puts the onus on Hamas. And he stopped short of calling for an immediate halt to the fighting as some European leaders have done. Mr Bush said: "I understand Israel's desire to protect itself, and that the situation now taking place in Gaza was caused by Hamas."