"All energies are focused on today," Saharkhiz, whose father, an adviser to Karroubi, is in jail.
Protesters, once again, filled the rooftops of Tehran Wednesday night chanting, "Allahu Akbar" ("God is greatest").
"They are loud and coming from everywhere," an observer who requested anonymity said. "It's been many weeks since this has happened."
The chants were first heard before the 1979 revolution, as people called out against the regime of the late Mohammad-Reza Shah Pahlavi. The custom was renewed last summer after the contested elections.
The opposition claims that Ahmadinejad's victory in the June 12 election was fraudulent and that the true winner was opposition leader Mir Hossein Mousavi. Hundreds of thousands marched in the streets against the government in the weeks after the vote, prompting a massive wave of arrests.
Nevertheless, the opposition has succeeded in continuing to hold regular protests, often timing them to coincide with days of important political or religious significance in attempts to embarrass authorities. The tone of the rallies has shifted from outrage about alleged fraud in Ahmadinejad's re-election to wider calls against the entire Islamic system, including Khamenei.
Tensions have mounted further since the last large-scale marches, in late December, which brought the most violent battles with security riots in months. At least eight people were killed in clashes between protesters and police, and security forces have intensified arrests in the weeks since.
Jim Sciutto, Lara Setrakian and The Associated Press contributed to this report.