BEIRUT — Tensions were running high on Monday on the Israel and Lebanon border after an Israeli military thwarted an operation carried out by Hezbollah. Israel says it has fired on Hezbollah militants who crept into its territory, in what Israel"s prime minister called a "serious security incident". The Israel Defense Forces (IDF) said up to four militants crossed the border in the Mount Dov area, part of the Israeli-occupied Syrian Golan Heights. The IDF said "the terrorists fled back to Lebanon" after being shot at. The area has been tense for days after a Hezbollah fighter was killed in an alleged Israeli airstrike in Syria. Israel, which has neither confirmed nor denied it carried out the strike in the early hours of last Monday, had warned Hezbollah not to retaliate. Hezbollah’s attack was made in retaliation for the death of one of its fighters, killed in an apparent Israeli strike on the edge of Damascus last Monday, according to a Lebanese source. “Lebanon and Hezbollah will bear the responsibility for any attack from Lebanese territory,” Israeli Prime Minister Benjamin Netanyahu said in broadcast remarks, shortly before the reports of the incident. Israeli media, citing unnamed military sources, said the Hezbollah cell was planning to attack an IDF post. The reports said Israel had been tracking them and its forces opened fire once the militants crossed the so-called Blue Line — the UN-recognized boundary between Israel and Lebanon. Reports say the Israeli army fired artillery shells in their wake. There are no reports of casualties on the Lebanese side, BBC reported