Russia's new anti-terrorism laws, which include measures imposing sweeping restrictions on Christian evangelising and teaching the faith, have officially come into force.

The 'Yaroyava' package, named after their sponsor in the Russian Duma, has been fiercely condemned both by Russian Christians and rights activists and internationally. It makes house churches illegal and limits religious activity to registered buildings.

According to Russia's Council of Churches-Baptists, the laws will "create conditions for the repression of all Christians". The council said in an open letter: "Any person who mentions their religious view or reflections out loud or puts them in writing, without the relevant documents, could be accused of illegal missionary activity."

Another open letter, from the Protestant Churches of Russia, said the laws were "the most draconian anti-religion bill to be proposed in Russia since Nikita Khrushchev promised to eliminate Christianity in the Soviet Union".

One of the signatories to the letter, Mission Eurasia president Sergey Rakhuba, said in a statement from the organisation: "We don't know yet how these laws will be implemented, but it is already clear that they are achieving their goal of creating an atmosphere of fear and suspicion within society, while allowing the government to restrict freedom in violation of the Constitution and international norms.

"Believers will soon need to make a very important choice: whether to obey God or these new Russian 'laws.'"

However, while the new laws have the potential to be extremely disruptive for Protestant Christians and other religious minorities in Russia, some observers believe their implementation may be patchy. Release International chief executive Paul Robinson said: "Let's wait and see what actually happens in terms of implementation on the ground. There is often a temptation in these situations to immediately fear the worst."

However, he added: "Having said that, we need to pray for Russian brothers and sisters now, as it's possible the doors may well be closing on the freedoms the church in Russia currently enjoys."

Some rights groups are considering legal appeals against the legislation as they regard it as unconstitutional.