The Israeli navy arrested four Palestinian fishermen on Sunday in the Mediterranean off the Gaza Strip, the territory's ruling Islamist movement Hamas said.

"This morning, four fishermen -- Najid Bakar and his sons Omran, Fahdi and Mohammad -- were arrested by the Israeli navy while fishing west of Gaza City," a source at the Hamas interior ministry said.

An Israeli military spokesman told AFP that a naval vessel had "fired warning shots" and "four Palestinians were subsequently arrested for questioning since they were in an area closed to fishing."

Israel has imposed a naval blockade around the Gaza Strip and permits a fishing zone of three nautical miles (about 5.5 kilometres) for the Palestinians.