"The timing and targeting of the campaigns suggest that the attacks are politically motivated in connection with the Iranian presidential election on Friday," Google vice president of security engineering Eric Grosse said in a blog post.
"These campaigns, which originate from within Iran, represent a significant jump in the overall volume of phishing activity in the region."
For nearly three weeks, California-based Google has been fighting "phishing" email messages crafted to trick recipients into clicking on links leading to phony account maintenance web pages that steal user names and passwords.
The ruse was "aimed at compromising the accounts owned by tens of thousands of Iranian users," Grosse said.
There were indications that the same culprits were involved in a cyberattack targeting Iranians about two years ago, according to Google.
"In this case, the phishing technique we detected is more routine; users receive an email containing a link to a web page that purports to provide a way to perform account maintenance," Grosse said.
"If a user clicks the link, they see a fake Google sign-in page that will steal their username and password."
Google policy is to notify targets of state-sponsored attacks or other suspicious activity, along with working internally to thwart hackers, according to Grosse.
"Especially if you are in Iran, we encourage you to take extra steps to protect your account," Grosse said.
His suggestions included opting for two-factor verification that requires information other than a password to get into an account and checking that website addresses are legitimate.