A powerful hard-line Iranian cleric on Friday called for the execution of more opposition activists to silence anti-government protests, praising the hanging a day earlier of two men caught up in the leadership's postelection crackdown.

Speaking in a Friday prayer sermon, Ayatollah Ahmad Jannati said the wave of street demonstrations sparked by the disputed June presidential election would not have lasted until now if protesters had been executed early on.

"Whatever we suffered was because of our weakness. How many did the judiciary execute on July 9?" he said, referring to one of the particularly large protest days.

"We showed weakness, so then we had Ashoura," he said, referring to a major protest on Dec. 27. "If you show weakness now, the future will be worse ... There is no room for Islamic mercy."

Iran's judiciary is stepping up death sentences as the leadership intensifies its campaign to eliminate the challenge from the pro-reform opposition movement. Authorities announced Thursday that nine people accused of involvement in protests have been sentenced to death — including five who allegedly had a role in the Dec. 27 protests, which saw a particularly violent clampdown.

SLIDESHOW (Warning: GRAPHIC): Photos From the Violent Clashes

Iran's top prosecutor said a new group of protesters and others would soon be brought to trial.

The two men executed Thursday were arrested before the June 12 election on charges of belonging to an armed group aiming to topple the government. But authorities lumped them in with opposition activists arrested during the postelection crackdown.

In his sermon, aired live on state radio, Jannati thanked Iran's judiciary chief, Sadeq Larijani, for Thursday's executions and urged more, saying: "Stand up courageously for the sake of God, the same way you executed these two persons very quickly."

Jannati cited verses from the Quran, Islam's holy book, that he said show Islam permits rulers to kill their opponents, including "hypocrites, those with evil intentions and those who spread rumors."

Jannati is one of the best known hard-line clerics in Iran and frequently delivers the nation's keynote sermon during prayers on Friday. He holds positions on one of the powerful councils of clerics that under Iran's Islamic Republic system vets laws passed by parliament and controls who can run for the legislature.

Hard-liners have called for the trial and execution of Iran's opposition leaders including Mir Hossein Mousavi and former reformist president Mohammad Khatami and former parliamentary speaker Mahdi Karroubi.

Hundreds have been arrested in the heavy crackdown by security forces against opposition protests, but activists have continued to hold sporadic, large street rallies. The opposition says President Mahmoud Ahmadinejad's victory in the June election was fraudulent and call for his removal — though some in the movement have expanded to criticize Iran's clerical leadership.

The two men who were executed — Mohammad Reza Ali Zamani, 37, and Arash Rahmanipour, 20 — were convicted by a Revolutionary Court of belonging to "counterrevolutionary and monarchist groups," plotting to overthrow "the Islamic establishment" and planning assassinations and bombings.

They were arrested months before the election. But they were put on the same mass trial as around 100 opposition activists, protesters and politicians who were arrested in the postelection crackdown — an attempt by the leadership to show that the political opposition is in league with violent armed groups in a foreign-backed plot to overthrow the Islamic system.