(CNN) -- Children are bearing the brunt of the conflict in Gaza as the Israeli offensive to flush out Hamas fighters leaves youngsters battling indelible trauma while threatening the lives of newborns and their mothers, a senior aid official says.
Palestinians carry a boy wounded in an Israeli military strike to hospital on January 14.
Ann Veneman, executive director of the United Nations' children body UNICEF, says too little is being done to protect Gaza's children, who account for half the territory's population, from the horrors of the latest conflict.
More than 320 children have been killed and 1,500 injured in Gaza since the current conflict began more than three weeks ago, she says, a situation she has described as tragic and unacceptable.
"They are the innocent victims," she told CNN in Johannesburg, South Africa, before the launch of UNICEF's annual "State of the World's Children" report.
Children are particularly vulnerable in Gaza because families are trapped in the conflict areas. "People cannot leave and be a refugee and find safe haven in another country," she said.
Because they cannot escape the constant violence, Veneman says, most Gaza kids are severely traumatized.
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UNICEF is airing radio spots on the Gaza airwaves that advise parents on how to comfort their upset and terrified children. Also, UNICEF has teams on standby to offer psychological support to families.
Newborns and pregnant women in Gaza also are a concern, UNICEF says.
With hospitals and doctors already battling to cope with the injured, women and their newborns are not getting the medical attention they need. Inadequate medical supplies and severe shortages of food, water, diapers and formula worsen the already dire situation.
Power outages also endanger sick babies in neo-natal care.
A spokesman says that the Gaza headquarters of the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) has been hit by shells containing white phosphorus. 

Ban Ki-moon, the United Nations (UN) Secretary-General, expressed "strong protest and outrage" to the Israeli Government over the attack. "The number of casualties has reached an unbearable point," said Ban.

Ehud Olmert responded by saying that there were Palestinian fighters in the compound, launching mortars at Israeli troops.

"We do not want such incidents to take place and I am sorry for it but I don’t know if you know, but Hamas fired from the UNRWA site. This is a sad incident and I apologise for it," Olmert said.

A previous accusation was made against the UN after another UN building housing refugees was hit by Israeli tank shells a week ago.  According to UNRWA official Christopher Gunness, the accusation was later retracted by the Israeli government.

Ehud Barak, the Israeli Defence Minister, said it was "a grave mistake".

Along with UNRWA headquarters, a Palestinian hospital was set ablaze, and a media headquarters housing the Reuters news agency and other Palestinian reporters was also hit wounding two cameramen.  Around 500 people were sheltering in the Al-Quds hospital when it was bombed by Israel and hospital officials say they were hit with white phosphorus, a substance which sparks fires which cannot be put out by water and which causes serious burns and respiratory problems to anyone who comes in contact with it.

Adnan Abu Hasna, a spokesman for UNRWA, said fires were still raging hours after the attack and "tens of millions of dollars worth of aid" had been destroyed.  

Christopher Gunness issued a statement on the attacks saying, "There have been three hits on the UNRWA headquarters, the UNRWA compound in Gaza, including, I’m told by UNRWA head John Ging, white phosphorus. Three of our staff members have been injured. The workshop in our compound is in flames, and nearby are loaded fuel tankers. So the situation is extremely dangerous and extremely serious. We have been on the phone to the Israeli authorities, asking them to call off their fire from around the compound of a neutral international organization. We have not had the answer we want."  UNRWA reports that the fire at the compound will destroy tons of medical and food aid.  

United Nations Children's Fund joined the Red Cross in speaking out against the violence today, saying the deaths of children in Gaza were unacceptable.