By Laila Bassam and Tom Perry
BEIRUT (Reuters) - Lebanon's Hezbollah was bracing for the risk of Israeli military escalation when its old foe struck a blow it hadn't seen coming, plunging the Iran-backed group into hours of unprecedented disarray, sources familiar with Hezbollah operations say.
The explosion of thousands of pagers carried by Hezbollah fighters, medics and others sparked confusion and panic in the group known for military discipline and order. Some tossed away their devices as blasts echoed through Hezbollah-controlled areas of Beirut and other parts of Lebanon. Others buried them.
A Hezbollah official said that as the attack began, the group quickly raised its level of military readiness in case it was the opening shot in a bigger offensive by Israel, which has stepped up warnings of escalation in the conflict which has been raging across the border for a year.
Hezbollah leaders - who didn't carry the devices - turned to the group's internal phone network to find out what was going on. Families of Hezbollah members struggled to locate relatives as the wounded were ferried to scores of hospitals.
Hezbollah officials have described the attack as the most serious security breach in the history of the group, which was established by Iran's Revolutionary Guards in 1982 to fight Israeli forces that had invaded Lebanon that year.
A source familiar with Hezbollah thinking said last week that the group had expected Israel to heighten its attacks in Lebanon, based on what the source described as Israeli "preparations for worse".
In the opening moments of Tuesday's explosions, the group had initially entered a state of confusion before absorbing the "massive, unexpected shock", a second source familiar with Hezbollah operations said.
The attack had not paralyzed Hezbollah, the source added.
Hezbollah has vowed revenge.
BODYGUARDS AMONG THE WOUNDED
Hundreds of its fighters have been wounded, mostly in Beirut rathern than frontline villages in southern Lebanon, a Hezbollah official said.
The official said many of the casualties are medics or people with administrative roles in Hezbollah institutions - or their relatives who happened to be nearby.
Some have lost their sight or had hands amputated, their attention having been drawn to their pagers by a buzzing sound before it exploded.
"This is a sword that went through the organisation's guts," said Mohanad Hage Ali, deputy director of research at the Beirut-based Carnegie Middle East Center.
The attack appeared to cause a pause in Hezbollah's cross-border attacks on Israel, which resumed on Wednesday afternoon with the group announcing it had fired rockets in retaliation for attacks on villages in south Lebanon and in support of Gaza.
Hezbollah's media office could not immediately be reached for comment.
Bodyguards of some of top Hezbollah figures are among the wounded, though there have been no reports of casualties among the leadership. Sources have said Secretary General Sayyed Hassan Nasrallah was unharmed.
A top Lebanese security source and another source said Israel had planted explosives in 5,000 pagers imported by Hezbollah. Israel has not claimed responsibility. The explosions killed at least 12 people, including eight Hezbollah members - six fighters, a nurse and an engineer - in addition to children.
The number of wounded stands at some 2,800, according to Lebanon's health minister.
A senior Lebanese official said the situation was difficult for Hezbollah but the group could absorb the impact and had not been paralysed by the attack. The official, who is allied to Hezbollah but part of the group, spoke on condition of anonymity because of the sensitivity of the topic.
Nasrallah is due to deliver a speech on Thursday. The sources said the speech had been timed to allow the group to build a fuller picture of the attack before the address.
With several Hezbollah fighters killed in Israeli airstrikes in southern Lebanon on Tuesday, it marked one of the deadliest days for the group since it began firing on Israel nearly one year ago in support of Palestinians in the Gaza Strip.