JERUSALEM Israeli soldiers backed by helicopters killed at least two gunmen who crossed the border from Lebanon on Monday, the military said, in a sign of a possible new front opening as Israel's forces battled Palestinian Hamas militants in Gaza.

Artillery shelling and gunfire were heard at Lebanon's southern border with Israel near the town of Dhayra, a correspondent for Hezbollah's Al-Manar TV said in a post on social media.

A security source and a local source said a group of men approached the border, with one firing at an Israeli observation post.

A Hezbollah official said the group had not mounted any operation into Israel. Officials from Hamas and Palestinian Islamic Jihad also denied involvement.

In a statement, the Israeli military said its soldiers "killed a number of armed suspects that infiltrated into Israeli territory from Lebanese territory". It did not elaborate on the number.

Military helicopters "are currently striking in the area", the statement added.

Israel's Army Radio gave the location as being near Adamit, across from the Lebanese border towns of Aalma El Chaeb and Zahajra.

A spokesperson for the U.N.'s peacekeeping mission in Lebanon said the force was aware of an incident at the southern border but did not have further details. Lebanon's army had no immediate comment.

(Reporting by Laila Bassam, Timour Azhari and Maya Gebeily in Beirut and Dan Williams in Jerusalem; Editing by Hugh Lawson and Nick Macfie)