GAZA, April 3 -- An apparent Israeli airstrike killed six international aid workers with the World Central Kitchen and their Palestinian driver, the charity said Tuesday, in a potentially major setback to efforts to deliver aid by sea to Gaza, where Israel's offensive against Hamas has pushed hundreds of thousands of Palestinians to the brink of starvation.

The food charity, founded by celebrity chef Jose Andres, said it was immediately suspending operations in the region.

The source of fire late Monday could not be independently confirmed. The Israeli military expressed "sincere sorrow" over the deaths while stopping short of accepting responsibility.

Rear Adm. Daniel Hagari, the top military spokesman, said that officials are reviewing...