Israeli forces preparing for the U.S. military’s pier to be built off Gaza’s coast came under mortar fire this week, highlighting the threat posed to everyone involved in the plan to provide aid by sea.

On Monday, a “small number of mortars landed in the vicinity of the marshaling yard area” on the coast, according to Pentagon spokesman Maj. Gen. Patrick Ryder. U.S. forces who construct the pier and causeway will not be in Gaza. They will stay in the Mediterranean Sea and would not have been in the location where the mortars hit.