Jerusalem - Israeli security forces closed two popular beaches yesterday to scour them for explosives after two barrels filled with munitions were found washed up on the shores of southern Israel.

As helicopters searched for other similar devices, officials said the finds represented a new terrorism tactic by Palestinian militants.

An Israeli police spokesman, Micky Rosenfeld, said the barrels, each carrying 22 pounds of explosives, were intended either to strike a patrol boat or to make their way on to the shore and harm Israelis.

The first barrel was found on the beach of the port city of Ashkelon late Monday, and the second hours later in Ashdod, some kilometres to the north.

An explosives unit defused the first barrel, and the second blew up while a robot was inspecting it.

The beaches in both cities remained closed yesterday.

"Searches still continue all the way up the coast, past Tel Aviv and in the northern coast of the country," Mr Rosenfeld said.

An Israeli military analyst, Reuven Pedhazur, said it was unclear if the barrels had been intended by militants to wash up when they did.

"It could be there was a problem in the planning," he said.

He left open the possibility that the barrels were being used to smuggle explosives.

In Gaza, a spokesman for the military wing of Islamic Jihad told Reuters that the explosive devices were part of a joint operation of the group with two other factions, the Popular Resistance Committee and the al-Aqsa Martyrs Brigades.

The Popular Resistance Committee's Abu Saed said that the barrels were an attack intended to avenge the killing of a Hamas operative last month.

"We confirm that there are still many of these charges in the ocean, and they haven't exploded yet," he told Associated Press.

But a commander of the al-Aqsa Martyrs Brigades in Gaza last night denied the group was involved.

Talal Awkal, a leading Gaza analyst, said he did not think the barrels had been dispatched in an attack against Israel.

"Maybe they were being used for smuggling," he said.

The discovery of the devices comes at a sensitive time after last month's killing of Hamas military commander Mahmoud al-Mabhouh in Dubai.

Hamas has blamed Israel for the killing and has said it will retaliate.