"For almost three weeks, we have detected and disrupted multiple email-based phishing campaigns," Eric Grosse, Google Inc.'s vice-president for security engineering, wrote in a post on Google's blog.
"The timing and targeting of the campaigns suggest that the attacks are politically motivated," Grosse said without elaborating.
The phishing campaigns are being launched inside Iran and represent a big surge in the region's hacking activity before Iran's presidential election Friday, Grosse said.
The hackers direct gmail users in Iran to fake account maintenance pages where they are asked to give their username and password, Grosse said.
Google used its Chrome browser to detect a phishing campaign in 2011, when a young Iranian student claimed he hacked gmail accounts belonging to anti-government dissidents in a personal "patriotic" initiative unconnected to the government.
Moderate cleric Hassan Rowhani has emerged as the favourite in Iran's presidential race, after former presidents Mohammad Khatami and Akbar Hashemi Rafsanjani threw their support behind him.
A former chief nuclear negotiator, Rowhani, is keen to transform Iran's damaged relations with the west.
Pro-reform candidate Mohammad Reza Aref pulled out of the contest, saying he was asked to do so by Khatami.
Presidential incumbent Mahmoud Ahmadinejad cannot run for a third term in office.