Tehran, March 6 -- Iran's supreme leader Ayatollah Ali Khamenei on Monday described the poisoning of schoolgirls during the last few months as an unforgivable crime.

Speaking at a tree-planting ceremony at his office, Khamenei called for the most severe penalties to be imposed on those responsible, Reuters reported.

Khamenei's statements come after new cases were recorded on March 5 in several regions, amid ambiguity surrounding the issue.

The first incident of mass poisoning was reported on November 30 last year. The illness which is so far unexplained has affected hundreds of students in recent months.

The Iranian authorities believe that these girls may have been poisoned and blame it on Tehran's enemies.

Although there have been ...