Germany - A branch of the German security service is monitoring a campaign by Salafist Muslims to give away 25 million Korans to see if it violates constitutional rules on religious freedom.
Ibrahim Abou Nagie, a Cologne-based preacher, says he wants to save non-Muslims from hell.
The interior ministry in North Rhine-Westphalia said the campaign was a form of aggressive proselytising.
So far, about 300,000 copies have been given away.
Salafists are very conservative Muslims who try to emulate the earliest followers of the Prophet Muhammad.
'Disturbing the peace'
The Office for the Protection of the Constitution in the state of North Rhine-Westphalia, which keeps extremist and violent groups under surveillance, has been monitoring Mr Abou Nagie's organisation.
Parties from across the political spectrum united to criticise the Koran giveaway.
"Wherever possible, this aggressive action must be stopped," said Guenter Krings of the governing centre-right Christian Democratic Union (CDU), in an interview with the Rheinische Post newspaper.
He admitted that handing out religious material was not in itself objectionable, but said the Salafist radicals were disturbing the religious piece with their behaviour.
The centre-left Social Democrats and the Green Party have also expressed their concern.
Salafists have been handing out the German-language copies of Islam's holy books in the pedestrianised zones of cities, including Cologne.
"What is presented as the simple distribution of the Koran is in truth the subtle spreading of the Salafist ideology," said a spokesman for the state interior ministry of North Rhine-Westphalia.
Additional copies are also being distributed in Austria and Switzerland.
Last summer, the president of the Office for the Protection of the Constitution, Heinz Fromm, said: "Not all Salafists are terrorists.
"But almost all the terrorists we know about had contacts with Salafists or are Salafists themselves."
The project has been funded by Muslims buying a copy of the Koran which then funds the production of a second one to be given away.
Wealthy donors based in Bahrain have also made contributions.