As Israeli tanks rolled into Gaza on Wednesday heralding a new ground invasion, a UN building was destroyed in a bombing, killing one UN staff member and injuring 5 others, some of them 'very severely.'

The Israel Defense Forces denied targeting the building, claiming the explosion occurred while UN personnel were clearing land mines. However the UN Office for Project Services, (UNOPS) the agency involved, denied this.

"It should be stressed that it was not through any action removing unexploded ordinance at the location," a statement issued by the UN body said.

"This was not an accident, this was an incident. What's happening in Gaza is unconscionable," the head of the UNOPS Jorge Moreira said Wednesday at a news conference in Brussells, according to a UNOPS statement  "I am shocked and devastated by this tragic news. I saw the absolute dedication of our team in Gaza last month. They and other UN workers and premises should never be targeted. My sincere condolences to all those affected."

"Attacks against humanitarian premises are a breach of international law," Moreira said.

The UN building that was destroyed was located in an isolated area, and its location was notified to Israel Defense Forces, the UN agency said. "These premises were well known by the Israel Defense Forces and they were 'deconflicted,' everyone knew who was working inside the premises, it was UN personnel, UNOPS personnel," the agency's chief said.

The death of the UNOPS member has taken the number of United Nations personnel killed in this week's offensive to six. "In the past few days, another five UNRWA staff have been confirmed killed, bringing the death toll to 284. They were teachers, doctors and nurses: serving the most vulnerable," Philippe Lazzarini, the UNRWA Commissioner-General posted on X on Thursday.

Meantime UNICEF said around a third of the victims of the more than 400 people killed in the deadly airstrikes carried out by Israel Air Force pilots on Tuesday were children.

"Reports and images emerging from the Gaza Strip following today's attacks are beyond horrifying. Hundreds of people have reportedly been killed, including more than 130 children, representing one of the largest single-day child death tolls in the last year," the Executive Director of UNICEF, Catherine Russell, said in a statement.

"Some of the strikes reportedly hit makeshift shelters with sleeping children and families, another deadly reminder that nowhere is safe in Gaza," the statement said.

"The latest attacks come as lifesaving aid remains blocked from entering Gaza, compounding the risks to children. It has been sixteen days since the last truck delivering humanitarian aid crossed into Gaza. In addition, electricity has been cut to the main desalination plant, significantly reducing the amount of potable water."

"Today, Gaza's one million children – who have endured more than 15 months of war – have been plunged back into a world of fear and death. The attacks and the violence must stop – now," UNICEF said. 

(Top image - file photo).