Russia has accused the UK of double standards on fighting terrorism after a British judge rejected its request to extradite a prominent Chechen rebel.
Zakayev vowed to continue fighting Russia's "criminal regime"
Judge Timothy Workman ruled on Thursday that rebel envoy Akhmed Zakayev would not get a fair trial in Russia and could even face torture if returned.
Moscow accuses Mr Zakayev, a former rebel field commander, of committing crimes from abduction to murder.
Relations had suffered a "serious blow", the Russian foreign ministry said.
"While speaking in favour of uprooting terrorism in all its forms... in reality [the UK] gives shelter to terrorists on its territory," it said.
Mr Zakayev was detained at London's Heathrow Airport in December 2002 after arriving from Denmark and was on bail up until Thursday's extradition verdict.
Speaking after his release, he vowed to continue to fight Russia's "criminal regime" and said he hoped to see Russian President Vladimir Putin eventually tried as a war criminal.
"Just as I had to defend myself against accusations I was a terrorist, I believe he will have to defend himself against charges he is a war criminal," Mr Zakayev said.
'No right to appeal'
Moscow's charges against Mr Zakayev relate to the first of two bloody wars fought by separatists in Chechnya, a tiny, mainly Muslim province in Russia's North Caucasus region.
Since the 1994-96 war, when he took part in dramatic rebel attacks such as the surprise capture of Grozny, Mr Zakayev has been a familiar face as the main envoy of Chechen separatist leader Aslan Maskhadov.
After the separatist leadership's ejection during the most recent war in 1999, a pro-Moscow Chechen leadership was installed.
Akhmad Kadyrov, elected Chechen president in a controversial ballot in October, condemned Thursday's verdict, saying the extradition should have been granted automatically.
"If there is a world coalition... against terrorists... as a Russian citizen, he should have been extradited at the first request from our
side," Mr Kadyrov said on Russian TV.