Iran regularly organises funerals for soldiers killed in the 1980-1988 war whose remains are either returned by its neighbour or found in former combat areas, which were mainly in Iran.

Mourners gathered in front of Tehran University around marquees erected on Enghelab (Revolution) Street to shelter the coffins of nearly 150 "loyal companions" under a scorching sun, according to AFP journalists.

Iranian media reported that the dead included two "volunteers" who went to fight in Syria where Iran provides military support to President Bashar al-Assad.

Of the 148 soldiers killed in the Iran-Iraq war, only 35 have been identified, the reports said.

Portraits of Iran's supreme leader Ayatollah Ali Khamenei were seen among the crowd along with white, red and pink gladiolas.

"It is our duty to listen to these messages of greatness, perseverance and resistance that awaken in us the sense of responsibility," the head of the country's judiciary, Ebrahim Raisi, told the crowd, referring to the "testaments" of soldiers before going into battle.

"We will revitalise ourselves with the blood of the martyrs. It is this blood that has watered the great fruitful tree of the Islamic revolution," he added.

Raisi struck a defiant tone as he spoke of recent tensions between Iran and the United States.

Washington has ratcheted up crippling economic sanctions on Tehran after the Islamic republic's forces shot down an unmanned US drone, following a series of attacks on tankers that the United States blamed on Iran.

"The blessed hand that attacked the American drone confirmed that to resist the enemy, the Islamic republic has no hesitation," he said.

"The Islamic republic recognises America as the main enemy before the Zionist regime (Israel) and, with all its might, is capable of leading them to repentance," Raisi said before the funeral procession began.