MOSCOW (AFP) - Police in central Russia have ordered local teachers to report on students who join opposition parties and commit other "extremist" acts, teachers and education officials said on Thursday.

The letter from the regional police in the Ulyanovsk region to the local education department was sent earlier this month, according to copies of the text published online.

The letter told the education department to instruct teachers "to inform interior ministry authorities about underage children who join public organisations, extremist movements and groups, and other informal youth organisations".

One teacher, who asked not to be named, told AFP that the letter was sent out after students were found attending a rally by The Other Russia, an informal opposition group to President Vladimir Putin that includes former chess king Garry Kasparov in its ranks.

Ms Irina Shiryayeva, an Ulyanovsk city education official in charge of teaching activities, said most instructors were surprised to received such a notice from the police.

"It surprised us a little bit," Ms Shiryayeva told AFP. "We mostly try to go about our work in a different manner, focusing on instilling patriotism instead."

She said the education department told teachers that this was part of the authorities' broader anti-extremism drive.

The Russian prosecutor's office cited the anti-extremism campaign on Thursday when explaining why more than a hundred Western-funded pro-democracy groups were raided by the police in the past few weeks.

Russia's relations with the West have suffered in the year since ex-KGB agent Putin won re-election to a third term in the face of protests against his rule, and then passed a raft of legislation limiting Russians' political rights.

Informants were widely used by the Soviet Communist Party for much of the 20th century, with neighbours reporting to the police about the activities of those they found to be unpatriotic.