The Israeli military said it does not comment on foreign reports.
The bomb blast injured the Hamas member on Sunday, destroying his car as he was about to get in.
"The bomb that targeted a Hamas member in Sidon is a dangerous beginning and it is not possible to be silent about it," said Nasrallah, leader of the Iran-backed Shia Hezbollah.
In a televised address, he said "all indications" pointed to Israel.
People inspect the car damaged in a bomb attack at Sidon in southern Lebanon on January 14, 2018
The leader of Lebanon's Hezbollah on Friday accused Israel of a bomb attack that wounded a member of the Palestinian group Hamas in the Lebanese city of Sidon, calling it an act of aggression.
