The Israeli army on Saturday reduced fishing space off the coast of the Gaza Strip to four nautical miles from the six miles agreed on as part of last summer's cease-fire agreement, Gaza's fishermen's union has said.

"The Israeli side asked Palestinian fishermen on Saturday not to exceed four nautical miles in plying their trade," union head Nizar Ayyash told The Anadolu Agency.

"Israelis also warned fishermen against venturing into the six nautical miles agreed on in last August's cease-fire agreement," Ayyash added.

He noted that the move constituted a major violation of a cease-fire deal signed in August of 2014 between Palestinian factions and Israel.

Earlier Saturday, Israeli naval forces shot and killed a 34-year-old Palestinian fisherman off the coast of Gaza.

Two other fishermen were also detained, according Ayyash.

Israeli authorities have yet to issue an official statement regarding the reduction of Gaza's fishing space.

Palestinian faction Hamas described the killing of the fisherman as yet a "new Israeli violation of the cease-fire agreement."

The Israeli navy routinely opens fire on Palestinian fishing boats under the pretext that they fish in unauthorized waters.

Last summer, Israel allowed Palestinian fishermen to ply their trade up to six nautical miles off the Gaza coast-as opposed to three miles previously.

A cease-fire reached in August between Israel and Palestinian factions ended 51 days of relentless Israeli attacks on the Gaza Strip, which killed over 2,160 Palestinians, mostly civilians.

Ever since Hamas-which Israel deems a "terrorist" organization-won the 2006 Palestinian legislative polls, the self-proclaimed Jewish state has imposed a tight land and sea blockade on the coastal strip.