Come presidential election time, the streets of central Tehran are usually wallpapered with the candidates’ names and faces, their banners swaying from buildings and streetlights. But this time around, the biggest banners bear no names, only a simple message: Vote on Friday. One common poster shows the bloody severed hand of Gen. Qassim Suleimani — the Iranian commander whose killing in an American drone strike in January 2020 brought throngs of Iranians into the streets in mourning — casting a white ballot.

“Do it for his sake,” the poster implores.

The message is unsubtle: Vote, and you support the Islamic Revolution for which General Suleimani gave his life. Don’t, and you undermine the whole system.

Since the revolution in 1979 toppled the monarchy, Iran has been run by parallel branches of the government. One is elected and the other is appointed, composed of the supreme leader and powerful councils of clerics.

But even those limited freedoms, which shrank after a contested election in 2009 led to widespread unrest, have nearly disappeared in this election cycle. The country is now moving increasingly toward what amounts to a one-party system whereby the top council of clerics that vets candidates eliminates anyone seen as a challenge to their conservative policies and views.

The Islamic Republic’s hierarchy has long used election turnout to try to bolster its legitimacy, pointing to robust voter participation as proof that Iranians really do choose their leaders. If voter turnout is low on Friday, that could be regarded as a sign of growing disaffection.

Iran’s supreme leader, Ayatollah Ali Khamenei, blamed Iran’s enemies and the foreign media for voter apathy in a live televised speech on Wednesday.

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Credit…Arash Khamooshi for The New York Times

Thus it was that Iman, 28, an information technology worker who was shopping for lamps in Tehran on Monday, said, “I will vote because the destiny of my nation is very important to me.”

He said he would vote for Ebrahim Raisi, the ultraconservative judiciary chief who appeared to have the only real chance of winning after the Guardian Council — the body of top clerics that vets the contenders — disqualified virtually all the other viable choices.

“You’re doing what? Really?” said his new wife Melika, 21, grabbing her husband’s arm in alarm. “If you vote for Raisi, we’re done,” she said, only half-joking. (Like some other voters interviewed for this article, they declined to give their full names, for fear of speaking too openly about politics.)

The wife rolled her eyes as her husband listed what he said were Mr. Raisi’s qualifications: promises to battle the corruption many Iranians say is crushing their economy; the forcefulness to stand up to the United States in renewed negotiations over limiting Iran’s nuclear program in exchange for lifting American sanctions, which are deepening those economic problems.

“I don’t believe in any of them,” said Melika, a computer engineer. “I’m just tired of all of it. I’m done.”

All across Tehran this week, Iranians were saying much the same thing.