GAZA CITY, Gaza Strip (AP) — Six people — including an Associated Press video journalist — were killed Wednesday when leftover ordnance believed to have been dropped in an Israeli airstrike blew up in the Gaza Strip.

Simone Camilli and his Palestinian translator, Ali Shehda Abu Afash, were covering the aftermath of the war between Israel and Islamic militants in Gaza when they were killed. The blast occurred as Gaza police engineers were trying to defuse unexploded ordnance fired by Israel.

Four police engineers also were killed, police said. Three people, including AP photographer Hatem Moussa, were badly injured.

Moussa told a colleague that they were filming the scene when an initial explosion went off. He said he was hit by shrapnel and began to run when there was a second blast, which knocked him out. He woke up in a hospital and later underwent surgery before he was transferred to a hospital in Israel for more advanced care.

Police officials in Gaza said the blast took place at a special site set up in the northern town of Beit Lahiya where authorities have collected unexploded ordnance to be defused. The cause of the blast was not immediately known.

Hamas police spokesman Ayman al-Batniji said there had clearly been a ‘mistake’ and there would be an investigation. He said the Palestinians collect unexploded munitions but usually get help from international experts in disposing of them. “We never deal with these things alone,” he said, adding that police believe only a small fraction of unexploded bombs from the recent fighting have been recovered.

An official said an Israeli tank shell caused the first explosion, triggering the more powerful secondary blast that included several bombs, including unexploded missiles dropped in Israeli airstrikes. The Israeli military carried out nearly 5,000 airstrikes in a month of fighting.

Hamas police posted photos of what it said was the site shortly before the explosion showing a senior bomb disposal expert surveying the area with piles of unexploded bombs behind him. Even after the blast, the lot, surrounded by a low wall, was strewn with piles of unexploded shells. There appeared to be about 10 missiles dropped by Israeli warplanes and dozens of tank shells.

Iyad al-Bouzm, a spokesman for Gaza’s Interior Ministry, estimated that Israel dropped about 10,000 tons of explosives on Gaza, including shells fired by tanks, artillery batteries and gunboats, as well as more powerful missiles delivered in airstrikes. He said there was no estimate on how many unexploded shells remained.

Camilli became the first foreign journalist killed in the Gaza conflict, which took more than 1,900 Palestinian lives and 67 on the Israeli side. According to the Committee to Protect Journalists, a U.S.-based press-freedom advocacy group, four Palestinian journalists or media workers were previously killed in the fighting.

The 35-year-old Italian national had worked for the AP since 2005, when he was hired in Rome. He relocated to Jerusalem in 2006, and often covered assignments in Gaza. He had been based recently in Beirut, returning to Gaza after the war began last month.

He is survived by a longtime partner and a 3-year-old daughter in Beirut, as well as his parents and two sisters.

Camilli is the 33rd AP staffer to die in pursuit of the news since AP was founded in 1846, and the second this year. On April 4, AP photographer Anja Niedringhaus was killed and veteran AP correspondent Kathy Gannon was badly wounded by a gunman in Afghanistan.

“Simone was well known throughout Europe, and especially to our video team in London, where his death has hit AP deeply,” Gary Pruitt, the AP’s chief executive, said in a memo to staffers.

“As all of you know, this has been a very difficult year for AP,” he said. “As conflict and violence grows around the world, our work becomes more important but also more dangerous. We take every precaution we can to protect the brave journalists who staff our front lines. I never cease to be amazed at their courage.”

He said the AP was providing assistance to Camilli’s family.

Pope Francis prayed for Camilli and Abu Afash aboard the papal plane en route to South Korea after he was informed of their deaths by the Rev. Federico Lombardi, the Vatican spokesman, who noted the tremendous risks taken by journalists in covering conflict.

Francis, who came to the back of the plane to greet the press, was clearly moved.

“I have to make a silent prayer for Simone Camilli, one of yours, who today left us in service. Let us pray in silence,” the pontiff said.

Abu Afash, a 36-year-old Gaza resident, is survived by his wife and two daughters, ages 7 and 2½. He often worked with the international media as a translator and news assistant, and worked as a part-time administrative assistant for Agence France-Presse.

Hundreds of people attended Abu Afash’s funeral in Gaza City. Mourners sobbed and shrieked in grief, with many people kissing Abu Afash on the forehead before his body was taken away for burial.

“He is not a journalist. He’s not a terrorist, nor a politician. He’s an innocent man who loves to help everyone,” said his wife, Shireen, a doctor who heads the neonatal unit at the al-Nasr Pediatrics Hospital in Gaza City and spent much of the war treating the wounded.

“He was happy to help the foreign journalists in the war. He was not afraid. He knew that if he died, he will go to heaven,” she said. The couple was to celebrate their eighth wedding anniversary in four days.

Camilli was remembered by colleagues as a consummate storyteller — a passionate and talented newsman with an eye for detail and the ability to convey events with powerful video images that touched people around the world.

Camilli loved reporting from Gaza so much that he recently turned down an assignment in Iraq to come to the seaside strip, said Najib Jobain, the AP’s chief producer in Gaza.

“He was my brother. I have known him for almost 10 years. He was so happy to be with me working in Gaza,” Jobain said. “He was asked, ‘Do you want to go to Irbil or Gaza?’ He said, ‘I’ll go to Gaza.'”

Diaa Hadid, a longtime colleague, described Camilli as warm and funny. “To think he is not here is really just too much,” she said.

Camilli began his career in Rome while still a university student at the Sapienza University, helping cover Pope John Paul II.

Over the years, he worked on major stories across Europe and the Middle East, including the independence of Kosovo, the war in Georgia, the arrest of Bosnian Serb military leader Radko Mladic, the 2006 war between Israel and Lebanon, Hamas’ takeover of Gaza, the resignation of Pope Benedict XVI. Most recently, he had covered the rise of the Islamic State in Iraq and the Syrian refugee crisis.

Chris Slaney, the former senior producer in Jerusalem, said he brought Camilli to the region during Israel’s war against Hezbollah in 2006, and “he immersed himself in the Middle East story, which unfortunately is mostly a story of conflict.”

Tomislav Skaro, the AP’s Middle East regional editor for video, said praised Camilli’s “incredible eye for detail” and said he was able to personalize stories and portray human drama.

“He was incredibly calm, mature beyond his age, gentle and the friend that everybody wants to have,” Skaro said.

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Federman reported from Jerusalem. Associated Press writer Karin Laub in Gaza City and Nicole Winfield aboard the papal plane contributed to this report.