Lebanese Information Minister Ziad Makary condemned the detonation of the pagers - used by Hezbollah and others in Lebanon to communicate - 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 warfare with Hezbollah since the start of the Gaza war last October, declined to respond to Reuters' questions about the detonations.
A Hezbollah official, speaking on condition of anonymity, said the detonation of the pagers was the "biggest security breach" the group had been subjected to in nearly a year of conflict with Israel.
Video reportedly showing device exploding in a bag- — Maha Yahya (@mahamyahya) #Lebanon #Israel pic.twitter.com/UHUiGklUy6September 17, 2024
Developments in Lebanon are extremely concerning, especially given the "extremely volatile" context, United Nations spokesman Stephane Dujarric said, adding that the UN deplores any civilian casualties.
Without commenting directly on the explosions in Lebanon, an Israeli military spokesman said the chief of staff, Major General Herzi Halevi, had 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 earlier confirmed in a statement the deaths of at least two of its fighters in the explosions and said it was conducting an investigation into their causes.
Hezbollah fighters have been using pagers as a low-tech means to try and avoid Israeli tracking of their locations, two sources familiar with the group's operations told Reuters earlier this year.
A pager is a wireless telecommunications device that receives and displays messages.
The pagers were detonated in southern Lebanon, the southern suburbs of Beirut known as Dahiyeh and the eastern Bekaa valley - all Hezbollah strongholds.
Lebanese Health Minister Firass Abiad said 2750 people had been wounded in the explosions, 200 of them critically.
Many of those hurt included Hezbollah fighters who are the sons of top officials from the armed group, two security sources told Reuters.
One of the fighters 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.
Lebanon's Health Ministry has called on all hospitals to be on alert to take in emergency patients. (AP PHOTO)
Lebanese broadcaster al-Jadeed cited Ammar as saying what happened was an Israeli aggression.
"We will deal with the enemy in the language it understands," he added.
Iranian ambassador to Lebanon Mojtaba Amani suffered a "superficial injury" in Tuesday's pager blasts and is under observation in hospital, Iran's Fars news agency said.
After Tuesday's blasts, a Reuters journalist saw ambulances rushing through the southern suburbs of the capital Beirut, a Hezbollah stronghold, amid widespread panic.
A security source said that devices were also exploding in the south of Lebanon.
At Mt Lebanon hospital, a Reuters reporter saw motorcycles rushing to the emergency room, where people with their hands bloodied were screaming in pain.
The head of the Nabatieh public hospital in the south of the country, Hassan Wazni, told Reuters that about 40 wounded people were being treated at his facility.
The wounds included injuries to the face, eyes and limbs.
Groups of people huddled at the entrance of buildings to check on people they knew who may have been wounded, the Reuters journalist said.
Regional broadcasters carrying CCTV footage which showed what appeared to be a small handheld device placed next to a grocery store cashier where an individual was paying spontaneously exploding.
In other footage, an explosion appeared to knock out someone standing at a fruit stand at a market area.
Lebanon's crisis operations centre, which is run by the health ministry, asked all medical workers to head to their respective hospitals to help cope with the massive numbers of wounded coming in for urgent care.
It said health care workers should not use pagers.
The health ministry called on all hospitals to be on alert to take in emergency patients.
tewith AP
