Israel's Mossad spy agency planted explosives inside 5,000 pagers imported by Lebanese group Hezbollah months before Tuesday's detonations, a senior Lebanese security source and another source have said.

The operation was an unprecedented Hezbollah security breach that saw thousands of pagers detonate across Lebanon, killing nine people and wounding nearly 3,000 others, including the group's fighters and Iran's envoy to Beirut.

The Lebanese security source said the pagers were from Taiwan-based Gold Apollo, but the company said in a statement it did not manufacture the devices. It said they were made by a company called BAC, which has a license to use its brand, but gave no more details.