"The response is inevitably coming. We cannot remain silent on a violation of this magnitude because it means the whole of Lebanon would be exposed," Hassan Nasrallah stated in a televised speech.
"The decision is now in the hands of the battlefield," he said in his second speech since the killing of Saleh al-Arouri on Tuesday.
"Fighters from all areas of the border... will be the ones responding to the dangerous violation in the (southern) suburbs (of Beirut)," he added.
Arouri was eliminated in a missile strike blamed on Israel, which has not claimed responsibility for the strike.
In an earlier speech on Wednesday, Nasrallah had already warned Israel against waging war on Lebanon, threatening that the group's response would be "without limits".
Nasrallah also accused Israel of underreporting its military losses in the war, claiming Hezbollah has released footage showing "tanks exploding... sometimes with soldiers sitting on top of them".
