"No safe place for civilians" in Gaza, UN says
* More than 500 killed in densely-populated enclave
* 121 children among the fatalities, UNICEF says
* More than 1.2 mln in Gaza have no or little water
* Ready-to-eat food stocks running low, WFP warns
* Three hospitals among 18 damaged health facilities
GENEVA, July 22 (Reuters) - Palestinian civilians in densely-populated Gaza have no place to hide from Israel's military offensive and children are paying the heaviest price, the United Nations said on Tuesday.
"There is literally no safe place for civilians," Jens Laerke, spokesman of the U.N. Office for Humanitarian Assistance (OCHA), told a news briefing in Geneva.
More than 500 people have been killed in the coastal enclave which has an estimated 4,500 people per square kilometer, Laerke said. The priority for aid agencies was protecting civilians and evacuating and treating the wounded.
Nearly 500 homes have been destroyed by Israeli air strikes and 100,000 people have sought shelter in schools of the U.N. Relief and Works Agency (UNRWA), where they need food, water and mattresses, he said.
Israel began air strikes on the coastal strip on July 8, saying it wanted to halt missile fire out of Gaza by Hamas militants, and launched a ground offensive last Thursday. Israel pounded targets across the Gaza Strip on Tuesday, dashing hopes of a pause in the fighting. Hamas rejected an Egyptian ceasefire proposal last week.
Twenty-nine Israelis, 27 of them soldiers, have died.
But the overwhelming majority of people killed so far in the conflict are Palestinians, including 121 Gaza children under age 18 who make up one-third of the total civilian casualties, Juliette Touma of the U.N. Children's Fund (UNICEF) said.
More than 900 Palestinian children are also reported to have been injured, according to UNICEF.
"According to an assessment by aid workers on ground at least 107,000 children need psycho-social support for the trauma they are experiencing such as death, injury or loss of their homes," Laerke said.
More than 1.2 million people in the enclave have no water or only limited access to water as power networks have been damaged or lack fuel for generators, he said.
"In addition, we do have reports of sewage flooding which is a threat to public health," he said.
The World Food Programme (WFP) has distributed emergency food rations and food vouchers to more than 90,000 people so far during the conflict, spokeswoman Elisabeth Byrs said.
"Ready to eat food stocks are running low in Gaza given the conflict has lasted two weeks and the needs are increasing," she said.
Supplies will be bought locally and also airlifted from Dubai.
The World Health Organisation (WHO) said that 18 health facilities in Gaza have been damaged, including three hospitals.
"There are critical concerns with hospital supplies, as both medicines and medical disposables are in serious shortage, both in ministry of health and ngo hospitals, due to the large number of casualties and serious shortages even before the escalation of violence," WHO spokeswoman Fadela Chaib said.
(Reporting by Stephanie Nebehay; Editing by Angus MacSwan)