Musavi said in a statement posted on the "Kaleme" website that the executions are a warning to the opposition ahead of the first anniversary of last year's disputed presidential vote. Both Musavi and reformist cleric Mehdi Karrubi have called on the opposition organize street rallies to mark the day.
"How is it that today the courts...suddenly on the eve of the month of Khordad ,the month of consciousness and seeking justice, hangs these five individuals with so many unanswered questions?! Is this the Alavi [a referral to Imam Ali] justice that we were searching for?"
Musavi also said that Iran's judiciary executed the five without providing "any clear explanations regarding their charges, prosecution procedure, and trials" to the people, which is similar to the "unjust trend" that in recent months has led to the sentencing of a number of Iranian citizens.
Rahnavard has also said that the executions seem to be aimed at intimidating the opposition. "Are these hasty executions aimed at frightening people on the anniversary of [the June 12 vote]?" she asked.
"The important question is whether these actions are for strengthening national unity or national breakdown and other negative consequences?"
Four of the executed prisoners from Iran's Kurdish minority were charged with being members of the Party of Free Life of Kurdistan (PJAK), which has in recent years clashed with Iranian forces.
Their executions have led to outrage among rights activists and intellectuals, and according to some unconfirmed reports a protest strike is planned in Iran's Kurdish cities for May 13.
Many are particularly angry over the execution of Kurdish teacher Farzad Kamangar, who had denied the charges against him. Some Iranians have paid their respects to Kamangar by changing their profile picture on Facebook to a picture of Kamangar and several videos in his tribute are making the rounds, including this one where he is seen with some of his pupils.
Iranian lawyer Khalil Bahramian, who represented at least two of the executed Kurdish prisoners, including Kamangar, told RFE/RL's Radio Farda on May 11 that the bodies of the four Kurds have not been delivered to the families for what officials have described as "security reasons."
"It's a real tragedy, what do [the authorities] want to do with the bodies? When they were alive you didn't tolerate them and killed them. Now that they're dead why do you deal with their bodies in this manner?" Bahramian said.
He added that he's been informed that the mother and sister of Shirin Alam-Hooli, who was among the executed, were detained. It is not clear whether they have been released or remain in detention.
Human Rights Watch said in a May 11 statement that at least 17 more Kurdish prisoners are at risk of execution in Iran.
-- Golnaz Esfandiari