Iran says it has carried out a second execution linked to the anti-government protests engulfing the country.

Majidreza Rahnavard was hanged "in public" early on Thursday in the city of Mashhad, the judiciary announced.

A court convicted him of the charge of "enmity against God" after finding he had stabbed to death two members of the paramilitary Basij Resistance Force.

Human rights groups have warned that protesters are being sentenced to death after sham trials with no due process.

"Rahnavard was sentenced to death based on coerced confessions, after a grossly unfair process and a show trial. This crime must be met with serious consequences for the Islamic Republic," tweeted Mahmood Amiry-Moghaddam, director of Norway-based Iran Human Rights.

"Thousands of detained protesters, and a dozen death sentences already issued. There is a serious risk of mass-execution of protesters," he added.

The first execution in connection with the unrest took place on Thursday, triggering international condemnation.

Mohsen Shekari, 23, was convicted of "enmity against God" after being found to have attacked a member of the Basij with a machete in the capital, Tehran.

The Basij is a loyalist volunteer force often deployed by Iranian authorities to suppress dissent.

The women-led protests against Iran's clerical establishment were sparked by the death in custody of Mahsa Amini, a 22-year-old woman who was detained by morality police on 13 September for allegedly wearing her hijab, or headscarf, "improperly".

They have spread to 161 cities in all 31 provinces and are seen as one of the most serious challenges to the Islamic Republic since the 1979 revolution.

Iran's leaders have portrayed the protests as "riots" instigated by the country's foreign enemies. However, the overwhelming majority of protesters have been unarmed and peaceful.

So far, at least 488 protesters have been killed by security forces and 18,259 others have been detained, according to the Human Rights Activists' News Agency (HRANA). It has also reported the deaths of 62 security personnel.