REUTERS -  Militant group Hezbollah promised to retaliate against Israel after accusing it of detonating pagers across Lebanon on Tuesday, killing nine people and wounding nearly 3,000 others who included fighters and Iran's envoy to Beirut.

Lebanese Information Minister Ziad Makary condemned the late-afternoon detonation of the pagers - handheld devices that Hezbollah and others in Lebanon use to send messages - as an "Israeli aggression". Hezbollah said Israel would receive "its fair punishment" for the blasts.

The Israeli military, which has been engaged in cross-border fighting with Iran-backed Hezbollah since the start of the Gaza war in October, declined to respond to questions about the detonations.

The death toll rose from eight to nine on Tuesday night while the number of injured remained at 2,750, Lebanon's health ministry said.

Hezbollah confirmed in an earlier statement that the deaths included at least two of its fighters and a young girl.

The pagers exploded in southern Lebanon, the southern suburbs of Beirut known as Dahiyeh and the eastern Bekaa Valley - all Hezbollah strongholds.

In one instance, closed-circuit surveillance video carried by regional broadcasters showed a person paying at a grocery store as what appeared to be a small handheld device placed next to the cashier exploded.

A Hezbollah official, speaking on condition of anonymity, said the incident was the "biggest security breach" for the group in nearly a year of conflict with Israel.

The New York Times reported that Israel hid explosive material in the Taiwan-made Gold Apollo pagers before they were imported to Lebanon, citing American and other officials briefed on the operation. The material was implanted next to the battery with a switch that could be triggered remotely to detonate.

The Palestinian militant group Hamas, which is waging war with Israel in Gaza, said the pager blasts were an "escalation" that will only lead Israel to "failure and defeat".

UN special coordinator for Lebanon Jeanine Hennis-Plasschaert deplored the attack in a statement and said it “marked an extremely concerning escalation” in the conflict.

Washington said it was not involved in the explosions and did not know who was responsible. The U.S. renewed calls for a diplomatic solution to tensions between Israel and Lebanon.

It urged Iran - which with its allies Hezbollah, Yemen's Houthis and armed groups in Iraq has formed an "Axis of Resistance" against Israeli and U.S. influence - not to take advantage of any incident to raise instability.

Without commenting directly on the explosions in Lebanon, an Israeli military spokesman said the chief of staff, Major General Herzi Halevi, met with senior officers on Tuesday evening to assess the situation. No policy change was announced but "vigilance must continue to be maintained", he said.

Hezbollah fighters have been using pagers as a low-tech means of communication in an attempt to evade Israeli location-tracking, two sources familiar with the group's operations told Reuters this year. A pager is a wireless telecommunications device that receives and displays messages.

Iran's ambassador to Lebanon, Mojtaba Amani, suffered a "superficial injury" in Tuesday's pager blasts and was under observation in hospital, Iran's semi-official Fars news agency said. Reuters could not immediately confirm the report.

The casualties included Hezbollah fighters who are the sons of top officials from the armed group, two security sources told Reuters. One of those killed was the son of a Hezbollah member of the Lebanese parliament, Ali Ammar, they said.

"This is not a security targeting of one, two or three people. This is a targeting of an entire nation," senior Hezbollah official Hussein Khalil said while paying his condolences for Ammar's son.

Air France announced late on Tuesday it was suspending flights connecting Paris with Beirut and Tel Aviv through Thursday due to security concerns.

Earlier on Tuesday, Israel's domestic security agency said it had foiled a plot by Hezbollah to assassinate a former senior defence official in the coming days.

Hezbollah has said it wants to avoid all-out conflict with Israel but that only an end to the Gaza war will stop the cross-border clashes. Gaza ceasefire efforts remain deadlocked after months of talks mediated by Qatar, Egypt and the United States.

While they saw a threat of escalation, experts were more skeptical, for now, about the potential for an imminent full-scale Israel-Hezbollah war, which the U.S. has sought to prevent and which it believes neither side wants.

After Tuesday's blasts, ambulances rushed through the southern suburbs of Beirut amid widespread panic.

At Mount Lebanon Hospital outside Beirut, a Reuters reporter saw motorcycles rushing to the emergency room and people with bloodied hands screaming in pain.

The head of the Nabatieh public hospital in the south of the country, Hassan Wazni, told Reuters that around 40 wounded people were being treated at his facility. The wounds included injuries to the face, eyes and limbs.

Hezbollah fired missiles at Israel immediately after the Oct. 7 attacks by Hamas gunmen on Israel that triggered the Gaza war. Hezbollah and Israel have been exchanging fire ever since, while avoiding a major escalation.

Hezbollah has lost more than 400 fighters in Israeli strikes over the past year, including its top commander Fuad Shukr in July.

Tens of thousands of people have been displaced from towns and villages on both sides of the border by the hostilities.

On Tuesday, Israel added to its formal war goals the return of citizens to their homes near the border with Lebanon.