The Gaza Humanitarian Foundation on Wednesday said a vehicle carrying aid workers was attacked by Hamas militants.
At least five people on the bus – which was carrying more than two dozen local Palestinians working with the US-backed initiative – were killed and several injured, according to a statement from the GHF. Several workers are believed to have been taken hostage.
"We condemn this heinous and deliberate attack in the strongest possible terms," the statement said. "These were aid workers. Humanitarians. Fathers, brothers, sons and friends, who were risking their lives every day to help others."
The GHF said it holds Hamas fully responsible for the attack, adding that the militant group has been threatening aid workers and civilians seeking assistance daily. It called on the international community to condemn Hamas.
The foundation said that despite the attack, it would continue to distribute aid in Gaza.
Israel eased an 11-week blockade on Gaza last month, but only a "teaspoon" of aid has entered the enclave, according to the GHF.
The controversial US and Israeli-backed private organisation is overhauling aid distribution in the strip. Protected by private US security contractors, the foundation has set up aid distribution sites around the enclave.
The US and Israel have claimed that the initiative is aimed at keeping aid out of the hands of Hamas, which they say has been stealing aid. Despite claims that the initiative will allow aid to be dispensed more securely, scores of Gazans have been killed at distribution sites, with local authorities blaming Israeli soldiers for firing on those queueing for assistance.
The GHF said on Saturday that it has distributed nine million meals since starting operations in Gaza.
