At least 40 people have been arrested as Iranian teachers held another round of nationwide protests demanding a fair pay and the release of their detained colleagues.

The demonstrators gathered in front of the Education Ministry building in Tehran on Thursday and its offices in various other cities to protest discriminatory regulations on a teacher ranking plan as well as the "continuous and systematic" suppression of union activists.

According to videos uploaded on social media, the security situation around the Ministry building was tense as security forces cordoned off the streets leading to the central building of the ministry and did not allow teachers to pass.

Videos from other cities show protesters shouting slogans against the education ministry and parliament with some demonstrators assailing its speaker, whose family’s recent shopping trip to Turkey has led to widespread condemnations.

The Coordination Council of Iranian Teachers’ Trade Associations said in its Telegram channel that at least 40 protesters were arrested until noon local time. It recently said in a statement that the teachers' movement "will not be subdued" by security and judicial crackdowns on union activists that have intensified in recent months, including sentencing them to four to 12 years in prison.

Teachers across Iran have staged several nationwide protests and strikes in the past six months and have vowed to continue protests until authorities meet their demands including, the implementation of decade-old legislation that would bring the salaries and pensions of 750,000 teachers in line with other civil servants.