The US and Israeli-backed Gaza Humanitarian Foundation said Thursday that at least eight people had been killed in an attack on its workers, which it blamed on the Palestinian militant group Hamas.
GHF had earlier given a toll of at least five killed in the attack, which took place late Wednesday in the southern Gaza Strip.
"We are still collecting more information on the deadly and unprovoked attack on our dedicated local team members and volunteers," GHF interim executive director John Acree said in a statement.
"As of now, we can confirm at least eight fatalities, multiple injuries, and we fear that some of our team members have been taken hostage."
In an earlier statement, GHF said a bus carrying more than two dozen members of it team, "local Palestinians working side by side with the US GHF team to deliver critical aid, were brutally attacked by Hamas".
It said the team was en route to one of the foundation's distribution centres west of Khan Yunis in the southern Gaza Strip.
"We carefully considered closing our sites today given the heightened security risks and safety concerns, but we decided that the best response to Hamas' cowardly murderers was to keep delivering food for the people of Gaza who are counting on us," Acree said in the group's update.
"We will not be deterred from our mission towards providing food security for the Palestinian people in Gaza."
An officially private effort with opaque funding and backed by Israel, GHF began operations on May 26 after Israel completely cut off supplies into Gaza for more than two months, sparking warnings of mass famine.
The United Nations and major aid groups have refused to cooperate with the foundation over concerns it was designed to cater to Israeli military objectives.
GHF claimed it had distributed nearly 2.6 million meals today and more than 18.6 million to date.