Lebanon's Hezbollah group has blamed Israel for the simultaneous explosion of pagers used by group militants that killed at least nine people, warning Israel will be punished.

"We hold the Israeli enemy fully responsible for this criminal aggression," the group said in a statement on Tuesday.

Israel "will certainly receive its just punishment for this sinful aggression", the statement said.

Hundreds of pagers used by Lebanese civilians and Hezbollah militants exploded across Lebanon, killing at least nine people and wounding at least 2,750 others including Iran's ambassador in Beirut.

Among the dead were the son of a Hezbollah lawmaker and the 10-year-old daughter of a member of the group.

The girl was killed when her father's pager exploded as she was standing beside him, her family and a source close to Hezbollah said.

Public Health Minister Firass Abiad said 2,750 people had been injured by exploding pagers — "more than 200 of them critically".

Iranian state television reported that Tehran's ambassador in Beirut Mojtaba Amani suffered "superficial" injuries in one of the explosions.

There was no immediate comment from the Israeli military on the blasts, which came just hours after Israel announced it was broadening the aims of the war to include its fight against Hezbollah along its border with Lebanon.