Separately, the Lebanese army said the devices were detonated from inside Israel and identified them as sensors used by the Israelis for spying.

'Espionage device'

For their part, United Nations peacekeepers, who began an investigation after the explosions occurred, said the blasts appeared to have been caused by the detonation of two underground sensors.

"These do look like some sort of espionage device," Michael Williams, the UN special co-ordinator for Lebanon, was quoted by the Reuters news agency as saying.

Unifil, the UN mission in Lebanon, said the devices appeared to have been left by Israeli forces during Israel's 2006 campaign against Hezbollah.

But Hassan Fadlallah, a Hezbollah deputy, accused the UN mission of "unacceptable bias" over the claim.

"On what basis can Unifil say that the appliances were installed in 2006? How did it discover this before [the end] of the investigation?" he said.

Israeli response

The Israeli army said the Lebanese allegations "do not warrant a serious response" and that Israeli forces would "continue to act to maintain calm on Israel's northern border".

More than 70 people have been arrested this year in Lebanon on suspicion of spying for Israel.

Unifil also said it had protested to the Israeli military about overflights by drones while the Lebanese army and the UN peacekeepers were investigating the blasts.

Lebanese army troops opened fire on the drones with machine gun and small-arms fire, the Unifil statement said.

Williams said the use of drones was an obvious violation of Lebanese sovereignty and 1701, the US Security Council resolution that ended the 2006 conflict.

Williams called the overflights were "not particularly helpful at a time of obvious tension in the south".