Reports from Web sites affiliated with Iranian opposition figures said members of the Islamic Revolutionary Guard Corps, members of the Basij paramilitary force and plain-clothed forces surrounded the home of Karroubi last week.
Karroubi was met by mobs of demonstrators allegedly firing shots into the air Friday, preventing him from leaving his home.
The Tehran branch of the Revolutionary Guards, however, denied responsibility for demonstrations against the opposition leader.
"The perpetrators of the gathering and shooting in front of Mehdi Karroubi's home were a group of individuals acting arbitrarily and were in no way connected with the Basij or Revolutionary Guards," Dutch broadcaster Radio Zamaneh quoted the statement as reading.
The violence reached its peak Friday on al-Qud Day in Iran. Ruhollah Khomeini, the founder of the Islamic Republic of Iran, declared the last Friday of Ramadan as a day to support the Palestinians.
Karroubi, along with former Iranian Prime Minister Mir Hossein Mousavi, emerged as leaders of an opposition movement in Iran following their failed bid to unseat Iranian President Mahmoud Ahmadinejad in contested elections in 2009.
Karroubi's home was vandalized last year.