At least nine people were killed and thousands of others were injured when handheld pagers exploded across Lebanon on Tuesday in an apparent targeting of Hezbollah members, according to Hezbollah officials.

Lebanon’s state-run National News Agency initially reported that “the handheld pagers system was detonated using advanced technology, and dozens of injuries were reported” in Beirut’s southern suburbs and other areas. Lebanon’s health minister later said at least nine people were killed and 2,750 wounded — 200 of them critically.

Among those injured when the pagers exploded included Iran’s ambassador in Lebanon, Iranian state media reported.

A security source in Lebanon told Reuters that the pagers were carried by members of Hezbollah. A Hezbollah official, speaking to the outlet on condition of anonymity, described the incident as a detonation that was the “biggest security breach” during the nearly year-long war with Israel. It wasn’t immediately clear who was responsible for the attack. While Hezbollah blamed Israel, the Israeli government has not commented.

HEZBOLLAH’S NEIGHBORS: ISRAELI BORDER COMMUNITY UNDER CONSTANT ATTACK FROM TERROR GROUP

Photos and videos from Beirut’s southern suburbs circulating on social media and in local media showed people lying on the pavement with wounds on their hands or near their pants pockets.

“Several hundred” people were wounded in all in different parts of Lebanon when the incident happened, The Associated Press cited a Hezbollah official as saying.

In a statement obtained by Reuters, Hezbollah confirmed that the blasts killed at least two of its fighters and a girl. 

The girl was the 9-year-old daughter of a Hezbollah fighter who was inside her parents’ home when the pagers exploded, the Times of Israel reported.

ISRAEL STRUCK BY LONG-RANGE MISSILE FROM YEMEN, 40 PROJECTILES FROM LEBANON IN EARLY MORNING ATTACKS

Hezbollah said the cause of the simultaneous explosions was under investigation.

Hezbollah members recently began using the pagers that exploded after the group’s leader ordered them to stop using cell phones over concern that Israeli intelligence could track the devices.

Hezbollah is an Islamic terrorist organization that has long had the backing of Iran.

UN Special Coordinator for Lebanon Jeanine Hennis-Plasschaert said Tuesday that she deplores the attack across Lebanon that left at least nine dead, including children, and thousands injured.

In accordance with international humanitarian law, she reminded all concerned actors that civilians are not targets and must be protected at all times.

“Even one civilian casualty is one too many,” a statement from her office read. “The developments today mark an extremely concerning escalation in what is an already unacceptably volatile context. While the full impact of the attack is still unfolding, Hennis-Plasschaert urges all concerned actors to refrain from any further action, or bellicose rhetoric, which could trigger a wider conflagration that nobody can afford.

“The Special Coordinator underlines the urgency of restoring calm and calls on all concerned actors to prioritize stability as paramount. Too much is at stake to do anything less,” the statement added.

U.S. State Department spokesman Matt Miller denied that the U.S. was involved or had any knowledge of the incident prior to the explosions.

“I can tell you that the U.S. was not involved in it. The U.S. was not aware of this incident in advance,” Miller told reporters, adding that the U.S. is gathering information on the incident. 

White House press secretary Karine Jean-Pierre told reporters Tuesday that the U.S. was not involved in the attack. She also said the White House was not aware of the operation or the incident.

Pentagon press secretary Maj. Gen. Pat Ryder also held a weekly press briefing Tuesday and echoed Jean-Pierre’s comments, saying there was no U.S. involvement, to his knowledge.

The incident comes at a time of heightened tensions between Lebanon and Israel. The Lebanese militant group Hezbollah and Israeli forces have been clashing near-daily for more than 11 months against the backdrop of war between Israel and Hezbollah ally Hamas in Gaza.

This is a developing news story; check back for updates.

The Associated Press contributed to this report.