The Iranian government says suspected poisoning cases among schoolgirls have been reported in more than 50 schools in the country.

Concerns are growing among parents and students as the cause remains unknown.

Iran's Ministry of Interior issued a statement that there have been reports of complications in some students in 52 schools. It also stressed that the public that the issue of the poisoning is being seriously followed up.

Some schoolgirls complained of nausea, breathing problems and numb limbs, among other symptoms, on Sunday. Toxic substances are believed to be the cause.

The cases started appearing in November. More than 1,000 schoolgirls across the country have reportedly complained of what appear to be symptoms of poisoning.

The Iranian government has indicated that forces attempting to destabilize the country are behind the incidents. But local media have reported the suspected involvement of groups that are hostile to women's education.

Iran's education minister Yousef Nouri offered an apology on state-run television on Sunday, saying he understood parents' anxiety. He added he had instructed school officials to provide sufficient explanations.

Residents in Tehran expressed anger and frustration. One said such incidents are unacceptable in this age. Another called on the government to act quickly to protect the lives of the next generation, saying all the mothers in Iran are feeling distressed over the poisonings.