Thousands chanting “death to Israel” and “death to America” marched on Friday in a funeral procession in Tehran, for the seven Revolutionary Guard members killed in an airstrike widely attributed to Israel that destroyed Iran’s consulate in the Syrian capital Damascus.

The march, with protests in other Iranian cities, came at a time of heightened concerns about possible retaliation by Iran for Monday’s strike that killed 12 people, including four Syrian citizens and a member of the Lebanese militant Hezbollah group, according to officials.

The protesters in the capital headed to Tehran University, where the commander of the powerful Revolutionary Guard, General Hossein Salami, gave a speech.

He said that “no threat will go unanswered” in retaliation for Israel’s apparent strike.

“The collapse of (the Zionist regime) is very possible and close with God’s grace,” Salami said, adding that the US has become “wildly hated by the world”, especially in Muslim-dominated countries.

The public funeral coincided with Iran’s annual rally on Quds Day, or Jerusalem Day, a traditional show of support for the Palestinians that has been held on the last Friday of the holy month of Ramadan since the 1979 Islamic Revolution.

State TV live broadcast showed thousands of Iranians in Tehran following the truck carrying the bodies of the two generals and five officers to the cemetery, some waving flags of the Islamic Republic of Iran.

Iranian leaders have repeated promises of revenge. On Wednesday Iran’s President Ebrahim Raisi said the attack “will not remain without answer”.

By attacking an Iranian diplomatic station, Israel’s apparent escalation has raised fears that the devastating six-month war against Hamas could spill over into the entire Middle East and beyond.

Israel faces increasing isolation as international criticism mounts over its killing of foreign aid workers this week who were trying to deliver desperately needed food in Gaza.

Iran does not recognise Israel and views it as its arch enemy. It also supports militant groups Hamas and Hezbollah.

Clashes between Israel and Hezbollah along the Israeli-Lebanese border have increased since the war in Gaza began nearly six months ago.