The Palestinian terrorist group Hamas attacked a bus full of aid workers with the Gaza Humanitarian Foundation (GHF) on Wednesday, killing at least five local Palestinians who worked with the group.

Several members of the group may also have been taken hostage.

In a statement, GHF said:

Tonight, at approximately 10 p.m. Gaza time, a bus carrying more than two-dozen members of the Gaza Humanitarian Foundation team, local Palestinians working side-by-side with the U.S. GHF team to deliver critical aid, were brutally attacked by Hamas. At the time of the attack, our team was en route to one of our distribution centers in the area west of Khan Younis.

We are still gathering facts, but what we know is devastating: there are at least five fatalities, multiple injuries, and fear that some of our team members may have been taken hostage. We condemn this heinous and deliberate attack in the strongest possible terms. These were aid workers. Humanitarians. Fathers, brothers, sons, and friends, who were risking their lives everyday to help others. Our hearts are broken and our thoughts and prayers are with every victim, every family, and every person still unaccounted for.

This attack did not happen in a vacuum. For days, Hamas has openly threatened our team, our aid workers, and the civilians who receive aid from us. These threats were met with silence.

The GHF holds Hamas fully responsible for taking the lives of our dedicated workers who have been distributing humanitarian aid to the Palestinian people at the foundation’s sites in central and southern Gaza.

Tonight, the world must see this for what it is: an attack on humanity. We call on the international community to immediately condemn Hamas for this unprovoked attack and continued threat against our people simply trying to feed the Palestinian people.

We will release additional information once it becomes available. Despite this heinous attack, we will continue our mission to provide critical aid to the people of Gaza.

Hamas is opposed to the group’s operations because Hamas prefers to steal aid provided by the United Nations and to use it to control the population of Gaza.

This story is developing.

Correction: the original version of this story reported that the workers who were attacked were Americans. They were local Palestinians working with the group.