Israel launched an investigation into a UN worker’s death in Gaza on Wednesday, a foreign ministry spokesman said, after the military denied responsibility for the deadly blast. The UN Office for Project Services (UNOPS) announced the death of one of its employees in Gaza when a United Nations building in the central city of Deir al-Balah was hit by an unidentified piece of “explosive ordnance”. The incident, which UNOPS said also left five people injured, came as Israel renewed its intense bombardment of the Palestinian territory, carrying out the deadliest wave of attacks since a January truce in its war against militant group Hamas. UNOPS chief Jorge Moreira da Silva said in a statement that he was “shocked and devastated” by the staff member’s death. “This was not an accident,” he said, adding that “attacks against humanitarian premises are a breach of international law” and that UN personnel and premises “must be protected by all sides”. Israeli foreign ministry spokesman Oren Marmorstein said in a statement on social media that “we express sorrow over the death of the Bulgarian citizen, a UN worker, today in the Gaza Strip”. “The circumstances of the incident are being investigated,” Marmorstein added, stressing that “the initial examination found no connection … whatsoever” to Israeli military activity. Bulgaria’s foreign ministry said that one of its citizens working for the United Nations was killed in Gaza, without specifying where in the territory. The wounded were taken to Al-Aqsa Martyrs hospital, AFPTV footage from Deir al-Balah showed. Marmorstein said Israeli troops were “assisting in evacuating the body and the wounded, who will be treated in hospitals in Israel”. United Nations Secretary General Antonio Guterres “was deeply saddened and shocked to learn of the death of a United Nations Office for Project Services staff member, when two UN guest houses in Deir al-Balah were hit in strikes”, said spokesman Farhan Haq. He added that at least 280 UN employees had been killed in Gaza since the war began in October 2023. AFPTV images showed two men who appeared to have leg injuries, and a third with bandages on both arms and his abdomen and traces of blood on his chest. Two of the injured were wearing bulletproof vests, with one wearing a T-shirt of UNMAS, the United Nations Mine Action Service, underneath. The health ministry in the Hamas-run territory earlier said an Israeli strike was to blame. An Army spokesperson told Agence France-Presse that “there was no IDF operational activity there and that the IDF didn’t strike the UN compound”. A UN source had initially said a second employee was killed. Haq said that was not the case, but that one of the five injured employees was in very critical condition. He did not provide the nationality of the dead employee. “The locations of all UN premises are known to the parties to the conflict, who are bound by international law to protect them and maintain their absolute inviolability,” Haq said. “The secretary general strongly condemns all attacks on UN personnel and calls for a full investigation,” he added. Haq said it was too early to “determine responsibility”, but that the explosion was not the result of a mine or unexploded ordnance, but rather an explosive that was “either dropped or fired at the infrastructure and detonated inside the building”. “We do not know whether it was fired from land, from the sea, from the air,” he said. Also on Wednesday, Israel said its troops retook part of a corridor that bisects Gaza, and its defence minister warned that attacks would intensify until Hamas frees dozens of hostages and gives up control of the territory. The military said it had retaken part of the Netzarim Corridor that divides northern Gaza from the south, and from where it had previously withdrawn as part of a ceasefire that began in January. That truce was shattered on Tuesday by Israeli air strikes that killed more than 400 Palestinians, mostly women and children, according to the Gaza Health Ministry. The advances on the ground by Israel on Wednesday – which included sending more troops to southern Gaza – threatened to drag the sides into all-out war again. The ceasefire had given war-weary Palestinians some respite, allowed a much-needed surge of humanitarian aid into Gaza – and led to the release of dozens of hostages who had been held for more than 15 months. Additional reporting by Associated Press