At least 51 Palestinians were killed Tuesday when Israeli tanks opened fire on aid seekers waiting for U.N. and commercial trucks to enter Gaza with desperately needed food, according to the Health Ministry.

Palestinian witnesses told The Associated Press that Israeli forces had fired on the crowds. The military did not immediately respond to a request for comment.

It did not appear to be related to a new Israeli- and U.S.-supported aid delivery network that rolled out last month and has been marred by controversy and violence.

Yousef Nofal, an eyewitness, said he saw many people motionless and bleeding on the ground after Israeli forces opened fire.

"It was a massacre," he said, adding that the soldiers continued firing on people as they fled from the area.