Iran has announced more than 100 arrests nationwide over the mystery poisonings of thousands of schoolgirls, charging that the unidentified alleged perpetrators may have links with "hostile" groups.

Recall, thousands of schoolgirls have suffered fainting, nausea, shortness of breath and other symptoms after reporting "unpleasant" odors on school premises, with some being treated in hospitals since late November.  

Iranian state-run media outlets reported late Saturday that the Iranian interior ministry announced the arrests over the suspected poison attacks in more than 200 schools that have sparked fear and anger among pupils and their parents.

"More than 100 people who were responsible for the recent school incidents were identified, arrested and investigated," the ministry said in a statement carried by state news agency IRNA.

"Among those arrested are people with hostile motives and with the aim of instilling terror in the people and students and to close schools."

The ministry added that "fortunately, from the middle of the last week until today, the number of incidents in schools has decreased significantly, and there have been no reports of sick students.”

The statement pointed at possible links to an Albania-based exiled Iranian opposition group that Tehran considers a “terrorist” organization, the People's Mujahedin of Iran or Mujahedeen-e-Khalq (MEK).

"The investigation of these criminal people, including the discovery of their possible connection with the terrorist organizations such as the MEK and others, is ongoing," IRNA reported.

More than 5,000 pupils have reportedly been affected in poisoning cases in approximately 230 schools across 25 out of Iran's 31 provinces.

The first suspected poisonings happened in November at a high school in the city of Qom which saw 18 schoolgirls hospitalized, according to Iranian state media.

The ministry said arrests were made in the provinces of Tehran, Qom and Gilan in the north, Razavi Khorasan in the northeast, West Azerbaijan, East Azerbaijan and Zanjan in the northwest, Kurdistan and Hamadan in the west, Khuzestan in the southwest and Fars in the south.

According to the Voice of America (VOA), Shahin Gobadi, Paris-based spokesman for the MEK, said the accusations were "a ridiculous show to cover up the role of the institutions under Khamenei's command in this big crime" and urged Tehran to accept an international investigation.

"The crime of poisoning thousands of schoolgirls... is the work of no one but the clerical regime and its security and repressive apparatus," he said in a statement.

CNN says both the United States and United Nations have called on Iranian authorities to fully investigate the suspected poisonings and hold those responsible to account.