Iran's supreme leader Ayatollah Ali Khamenei publicly condemned Wednesday for the first time the January 2 attack on Saudi Arabia's embassy in Tehran as "a very bad and wrong incident".

"Like the British embassy attack before it, this was against the country (Iran) and Islam, and I didn't like it," he added.

Britain's embassy in Tehran was attacked in 2011.

The arson attack on Saudi Arabia's embassy -- for which local media reports say as many as 140 people have been arrested -- led to Riyadh quickly severing diplomatic ties with Tehran.

The violence occurred hours after Saudi Arabia executed Shiite cleric and activist Nimr al-Nimr for crimes against the kingdom.

The attack was followed by a mob taking selfies and smartphone video footage of themselves holding items stolen from inside the building, causing deep embarrassment in Tehran.

President Hassan Rouhani and other officials condemned the attack -- seen by millions worldwide via social media -- within hours and he has urged speedy prosecutions of those involved.

Iranian authorities have said that those detained over the incident included its ringleader but no charges have been announced.

The cutting of relations set back efforts made by Rouhani's government since July, when a nuclear deal with the West was struck, to boost Iran's clout in international diplomacy, particularly in peace talks on Syria.