Israel's army announced new strikes on Hezbollah targets in Lebanon on Thursday, as warning sirens rang out in northern Israel, indicating possible incoming fire.

Hezbollah chief Sayyed Hassan Nasrallah said Thursday that Israel will receive "just punishment" for the communications device explosions that killed 37 people and wounded nearly 3,000 over two days.

Israel will face "tough retribution and just punishment, where it expects it and where it does not," Nasrallah said in his first speech since the blasts, adding that he would not give further details of the place, timing or nature of Hezbollah's response.

U.S. Defense Secretary Lloyd Austin announced Thursday that he spoke Wednesday with Israeli Minister of Defense Yoav Gallant to “review regional security developments and reiterate unwavering U.S. support for Israel in the face of threats from Iran, Lebanese Hezbollah, and Iran’s other regional partners.”

French President Emmanuel Macron has held phone talks with Speaker Nabih Berri and caretaker Prime Minister Najib Mikati over the deadly explosions that rocked Lebanon on Tuesday and Wednesday.

The Israeli military said on Thursday it struck six Hezbollah "terrorist infrastructure sites" and a weapons storage facility in southern Lebanon overnight, as fears grew of a full-blown war.

The air force "struck Hezbollah terrorist infrastructure sites in the areas of Chihine, Taybeh, Blida, Mays al-Jabal, Aitaroun and Kfarkela in southern Lebanon, as well as a Hezbollah weapons storage facility in the area of Khiam in southern Lebanon," a military statement said.

Sayyed Hashem Safieddine, the head of Hezbollah’s Executive Council, said Wednesday that the group will respond to Tuesday's pager explosion attack with “special punishment."

The group is in a “new confrontation with the enemy," Safieddine said.

Israeli forces in the northern region are continuing their offensive and defensive exercises, the Israeli army said on Wednesday.

Free Patriotic Movement leader Jebran Bassil described the pager explosions that rocked Lebanon as “an attack on entire Lebanon, not on a party or a sect in it.”

Caretaker Health Minister Firass Abiad said Wednesday that 12 people were killed after paging devices used by Hezbollah members exploded across Lebanon a day earlier, adding that some wounded were treated in Syria.

"After checking with all the hospitals," the toll was revised to 12 dead, Abiad told a news conference, putting the number of wounded between 2,750 and 2,800.

European Union's top diplomat Josep Borrell said Tuesday he would seek more information from Beirut, where he just traveled from, as he came before journalists just after news broke from Lebanon of several hundred people being wounded by pagers exploding, including members of Hezbollah.

Suspicion immediately fell on Israel, which earlier Tuesday stressed that halting Hezbollah's attacks on Israel's north to allow residents to return to their homes was now an official war goal.