The IDF launched Operation Northern Shield on Tuesday morning to expose and neutralize terror tunnels Hezbollah has constructed along the Israel-Lebanon border.
"The digging of the cross-border attack tunnels that the IDF has discovered, before the attack tunnels became operational and posed an imminent threat to the safety of Israeli civilians, constitutes a flagrant and severe violation of Israeli sovereignty", the army said in a statement.
In a message directed at elements of Hezbollah and the Lebanese army, the IDF said it "advises them to stay away from any offensive [tunnel] dug from Lebanese territory into Israeli territory".
IDF officials estimated the operation would last for a few weeks, but a response from Hezbollah could prolong it further.
Last year, Hezbollah's leader said any future conflict with Israel could take place inside Israeli territory, and there would be "no place that is out of reach of the rockets of the resistance or the boots of the resistance fighters".
He added that Israel has investigated the possibility of underground Hezbollah tunnels since 2013 and launched a task force which has been working for the last two years searching for them.
In September, the IDF unveiled eleven kilometers of what is planned to be a 130 kilometer defensive wall stretching the length of the Lebanon-Israel frontier, equipped with cameras in the hope of thwarting any attempt by its enemy Hezbollah to infiltrate and attack.
The latest operation comes a day after Israeli Prime Minister Benjamin Netanyahu met US Secretary of State Mike Pompeo in Brussels, where he was reported to have been updated on the anti-tunnel action.
The tunnels are concentrated in the area around Metula, a small Israeli town of around 1,000 people nestled against the border with Lebanon.
"The IDF will increase its forces in the Northern Command and is highly prepared for developments, if any", the announcement concludes, noting that "a number of areas near the security fence in the north of the country were declared a closed military zone". "The Hezbollah terrorist organization, which is behind the digging of the tunnels, continues to operate with the support and funding of Iran in order to carry out terror activity against Israeli citizens". The IDF has used various means to collapse or fill with material tunnels from the Gaza Strip.
Tensions are high between Israel and Hezbollah, which fought a month-long war in 2006.