Israel briefly detained four Palestinian fishermen off the Mediterranean coast of Gaza on Saturday, Palestinian and Israeli sources said.

The Israeli military said it apprehended four suspects after two Palestinian vessels strayed from the designated fishing zone in the northern Gaza Strip, "violating security restrictions". The navy fired at the boats when they failed to respond to instructions to halt, it added.

The secretary of the Gaza fishermen's syndicate, Nizar Ayyash, told Reuters there were at least three Israeli attacks on Gaza fishermen on Saturday -- all within the permitted fishing area.

In one of the incidents, he said, Israeli forces fired rubber bullets at a boat, wounding two of the four people aboard who were later hospitalized. In another, they seized a small boat after detaining the two fishermen on board, he added.

"We have recorded several violations against fishermen within the permitted fishing zone in the past weeks," said Ayyash.

Fishing is one of the biggest industries in the coastal enclave, home to some 2.3 million Palestinians.

Citing security concerns, Israel maintains a land, air and sea blockade of Gaza, which is governed by the Hamas movement. Boats are not allowed to stray beyond a fixed limit to the north towards Israel.