The chairman of the Fishermen's Association in Gaza, Nizar Ayyash, told reporters that the three men had died but he was unable to confirm what had caused the explosion on Sunday.

The Israel Defence Forces (IDF) said it had not targeted anyone.

"The IDF is not responsible for the incident, and our indications show that their deaths were caused by an explosion inside Gaza," said an Israeli military statement.

Israel Army Radio said the cause was a rocket launched by mistake by the radical Islamist Hamas movement ruling Gaza.

Israel imposes tight restrictions on the work of fishermen off the coast of the Gaza Sea, citing security reasons.

It says it combats attempts to smuggle weapons or raw materials for rockets into the coastal enclave, as part of the blockade it has imposed on the Strip along with Egypt since 2007.

Gaza has about 3000 fishermen, of whom only 800 work on some 700 boats.

Australian Associated Press