Israel-Gaza live updates: Israel moves troops to Lebanon border after pager attack

Sources confirmed to ABC News that Israel was responsible for the explosion of pagers across Lebanon on Tuesday.

The pagers began exploding around 3:30 p.m. local time, according to Hezbollah officials. An intelligence source familiar with the situation told ABC News that Israel has long been working to perfect this type of "supply chain interdiction attack."

A source described the attack as a “huge operation” that took between six and 12 months to plan, involving the use of informants and collaborators. Explosives were implanted inside the beepers, the source added.

At least 12 people were killed and at least 2,800 injured by the explosions, Lebanese health authorities said.

Hezbollah said 11 of its members were killed on Tuesday, though did not disclose the circumstances of their deaths. The militant group vowed retaliation against Israel.

-ABC News' Joe Simonetti, Josh Marglin and Jordana Miller

The Israel Defense Forces said four of its soldiers were killed fighting in southern Gaza on Tuesday.

Capt. Daniel Mimon Toaff, Staff Sgt. Agam Naim, Staff Sgt. Amit Bakri and Staff Sgt. Dotan Shimon were killed in combat, the IDF said in a statement.

One officer and two soldiers from the Shaked Battalion, Givati Brigade, were "severely injured" during the same incident, the statement said. Another two soldiers were "moderately injured."

An officer from the Givati Reconnaissance Unit was also "severely injured" in southern Gaza, the IDF said.

-ABC News' Jordana Miller

In a Wednesday morning statement, the Hezbollah militant group said it would continue operations to "support Gaza" and vowed a "reckoning" for Israel after Tuesday's "massacre" when more than 2,750 people were injured by exploding pagers in Lebanon.

Hezbollah blamed Israel for the operation, which killed at least nine civilians. Eleven Hezbollah members died on Tuesday, the group said, though -- as is typical in its statements -- did not specify how they died.

Hezbollah leader Hassan Nasrallah is set to speak on Thursday afternoon to address the situation.

Israel has not commented on its alleged involvement in Tuesday's explosions in Lebanon.

-ABC News' Nasser Atta and Ghazi Balkiz

The Israel Defense Forces said warplanes hit Hezbollah targets in six locations in southern Lebanon into Wednesday. Artillery strikes were also conducted, it added.

Israeli aircraft bombed "Hezbollah terrorist infrastructure" in the areas of Majdal Selm, Odaisseh, Markaba, Blida, Maroun El Ras and Chihine in southern Lebanon, the IDF said in a statement.

-ABC News' Jordana Miller