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.

Hezbollah war grows as the two sides trade new fire, Hezbollah's leader accuses Israel of crossing "red lines."

The AR-924 pager, advertised as "rugged," contains a rechargeable lithium battery and could receive texts of up to 100 characters. It also claimed to have up to 85 days of battery life, crucial in Lebanon, where electricity outages are commonplace following years of economic collapse.

The unprecedented attack, followed by explosions of walkie-talkies, comes after Israeli officials warned about escalating tensions on the Lebanese border.