Men rhythmically struck their chests, a traditional way of showing grief, as women in long black chadors wept. Shouts of "Death to America," and "Death to Zionism" could be heard from the crowd gathered in Bozorgmehr Square in the central city of Isfahan, where the soldiers were based.
The head of Iran's powerful Revolutionary Guard, Maj. Gen. Mohammad Ali Jafari, threatened to retaliate against neighboring Saudi Arabia and United Arab Emirates over the attack. Earlier, he claimed, without providing evidence, that the United States and Israel ordered Saudi Arabia and the Emirates to carry out the attack, which also wounded 12.
"The treacherous government of Saudi and Emirates should know that the patience of the Islamic Republic about your hidden support for criminals and Takfiri groups has come to an end and Iran will not tolerate it anymore," said Jafari in a speech to the crowd.
"We will get revenge for the blood of our martyrs from Saudi Arabia and Emirates," he said. He asked President Hassan Rouhani to give the Guard the freedom to retaliate.
Pegah Mohammadi, 19, a student, said she attended the funeral to say goodbye to heroes who sacrificed to provide security to the Iranian people. "They gave their blood to protect our borders, to bring us security and peace," she said.
Family members accompanied the bodies of their loved ones to Isfahan's Bagh Rezvan cemetery. Five of the dead Guard members will be buried there and the rest will be buried in nearby cities and towns in Isfahan province.
Wednesday's attack, claimed by Baluch separatists, killed both seasoned officers and younger soldiers, including a 20-year-old in the Isfahan-based Guard's forces. The assault killed members of the Guard's Imam Hussein division, which played a significant role in various battles during the 1980s Iran-Iraq war.
Attacks by Jaish al-Adl, or "Army of Justice," have increased in recent years. Since its founding in 2012, it has abducted or killed border guards in hit-and-run assaults from its havens in Pakistan. It kidnapped 11 Iranian border guards in October. Five later were returned to Iran and six remained held.
Jafari said Iran expects Pakistan to "punish" the group, which allegedly has taken refuge in the country's southwest. "If they do not punish them, our retaliatory measures will be carried out," he said. Jafari said the Pakistani government knows where the attackers are harbored and accused Pakistan security forces of supporting them.
Tehran immediately linked Wednesday's attack to a U.S.-led conference in Warsaw largely focused on Iran, just two days after the nation marked the 40th anniversary of its 1979 Islamic Revolution.
The bomb struck a bus traveling on a road between the cities of Khash and Zahedan, a mountainous region along the Pakistani border that is also near Afghanistan. Images after the blast published by semi-official news agencies showed the explosion tore the bus apart, as passers-by used the light of their cellphones to illuminate the debris.
The Guard, which answers only to Iran's Supreme Leader Ayatollah Ali Khamenei, issued a statement saying a vehicle loaded with explosives targeted a bus carrying border guards affiliated with its force.
Associated Press writer Nasser Karimi in Tehran contributed to this report.