BEIRUT, Sept 18 (Reuters) - Hand-held radios used by armed group Hezbollah detonated on Wednesday across Lebanon's south in the country's deadliest day since cross-border fighting erupted between the militants and Israel nearly a year ago, stoking tensions after similar explosions of the group's pagers the day before.

Taiwan's government and Bulgarian authorities Friday both denied making the exploding pagers used by Hezbollah in Lebanon.

According to reports from senior Lebanese security sources, the explosions were caused by small amounts of explosives hidden inside 5,000 Taiwan-made pagers ordered by Hezbollah five months before the incident.