JERUSALEM, Dec 31 (Reuters) - Israel's bombing along the Gaza Strip's border with Egypt aims to destroy Palestinian smuggling tunnels and will continue until that objective is achieved, an Israeli military official said on Wednesday.

Since an Israeli air offensive in Hamas-ruled Gaza began on Saturday, warplanes have made three major sorties over the 14km-long (9 mile) frontier, dropping bombs which penetrate the ground and then explode, Palestinian witnesses said.

A senior military official said the air force was using "bunker buster" bombs whose underground blasts sent shockwaves reaching hundreds of metres (yards) in every direction, enough to collapse tunnels and kill or incapacitate anyone inside them.

"The objective is to destroy all of the tunnels used to smuggle arms. If that has already been achieved, good, but if we spot someone popping up from another tunnel, I don't doubt we would go back in," the military official said.

Hundreds of the secret passages have allowed Hamas and other armed Palestinian factions to bring in arms from the Egyptian Sinai. They have also been a source of commercial goods, circumventing a crippling international embargo on Gaza.

Asked if the air force was trying not to hit any tunnels used exclusively for smuggling in non-military contraband, the Israeli official said: "There is no such thing. They're all dual-use." (Writing by Dan Williams; Editing by Giles Elgood) (For more stories on Gaza, please click on [nLO226261])

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