Iranian opposition leaders are under fire by the conservative leadership in Tehran after they petitioned to have demonstrations in solidarity with anti-government protests in the Middle East.
Karroubi and Mir Hossein Mousavi emerged as leaders of the so-called Green Movement that contested the 2009 re-election of Iranian President Mahmoud Ahmadinejad.
Reports last week suggested Mousavi was isolated from the outside world as masked guards replaced private security personnel at his home. Karroubi's Web site, Saham News, reports that intelligence forces cleared the way for attacks on his home.
"They broke the building's windows and threw three sound grenades inside the building," Dutch broadcaster Radio Zamaneh reports, citing the Web site.
Karroubi said he would maintain his resistance "to the last drop of my blood."
Karroubi and Mousavi have been under house arrest since early February. Karroubi's Web site added that his son and wife were apprehended by state security forces.
Iranian lawmakers last week called for the deaths of the two opposition leaders.