Livni told public radio that while she and the rest of the opposition welcomed the army's discovery of the tunnels and their eventual demolition, "the incident must be kept in proportion".

"We are not now in a situation where our soldiers are behind enemy lines," said Livni, who served as foreign minister during Israel's 2006 war with Hezbollah.

"We are talking about engineering activity within the sovereign territory of the state of Israel," she added, accusing Netanyahu of "blowing the incident out of proportion".

Israel announced on Tuesday that it had discovered Hezbollah tunnels infiltrating its territory from Lebanon and launched an operation to destroy them.

Army spokesman Lieutenant Colonel Jonathan Conricus said the "attack tunnels" dug by the Shiite militant group backed by Iran, Israel's main enemy, were not yet operational.

He declined to say how many had been detected or how they would be destroyed, but stressed all activities would take place within Israeli territory.

Netanyahu, whose electoral appeal rests to a large extent on his image as the Jewish state's "Mr Security", went on television on Tuesday evening to explain the tunnel threat, with armed forces chief of staff Lieutenant General Gadi Eisenkot at his side.

On Wednesday he told UN Secretary General Antonio Guterres on the phone that "he expects the UN to strongly condemn the violation of Israel's sovereignty," according to his office's Twitter account.

- Seeking to 'sow panic' -

Netanyahu also demanded the international community join in demands to "impose increased sanctions on Hezbollah", it added.

The Israeli leader is seeking to hold his governing coalition together after last month's resignation of defence minister Avigdor Lieberman over a controversial Gaza ceasefire, which left him clinging to a one-seat majority in parliament.

The prime minister took over the defence portfolio after Lieberman's resignation.

He has also faced mounting legal woes, with police on Sunday recommending that he and his wife Sara be indicted for bribery, the third such decision against the premier in recent months.

The army has dismissed any suggestion of political influence in the operation, but some in the opposition, while supporting the army's actions, have pointed to how Netanyahu handled the announcement.

Livni alleged that part of Netanyahu's thinking was to deflect criticism from residents of southern Israel who say he has failed to quash the threat of cross-border rocket fire from militants in the Gaza Strip.

"Therefore he made a defensive engineering event into a dramatic military operation," she said, giving two possible reasons for such a move.

"Either the prime minister is himself panicking or he wants to sow panic to justify his actions both in delaying elections and abandoning the residents of southern Israel."

Livni later told foreign journalists in a phone briefing that the international community should bring greater pressure on Lebanon over Hezbollah's activities.