Moscow (AFP) - Amnesty International said Wednesday Russian authorities had shut them out of their office in Moscow, with city authorities citing rent arrears.
The global human rights campaign group said that the locks had been changed and the alarm system switched off in the premises, which is its only office in Russia.
Amnesty International regularly criticises Russian authorities for overly harsh treatment of prisoners and urges the release of those jailed in cases it views as politically motivated.
"Staff found the office was sealed around 10 am (0700 GMT). The organisation had not received any warning and the premises was sealed in their absence," the rights group wrote on its website.
Amnesty regularly criticises Russian authorities for overly harsh treatment of prisoners and urges the release of those jailed in cases it views as politically motivated.
Most recently on Tuesday it called on the authorities to "end the pattern of impunity for torture and other ill treatment" after Russian activist Ildar Dadin, jailed for solo anti-Kremlin protests in Moscow, said he had been beaten and threatened in jail.
John Dalhuisen, the group's Europe director, said in a statement: "We do not know what prompted Moscow authorities to prevent our staff from accessing our offices -- an unwelcome surprise for which we received no prior warning."
He added that "given the current climate for civil society work in Russia, there are clearly any number of plausible explanations".
But he said he was hopeful that there was a "simple administrative explanation".
Moscow's municipal property department said in a statement quoted by RIA Novosti state news agency that Amnesty had been informed of "significant violations over rent payment" and had been given a month to pay up or have its rent agreement torn up but had ignored the demand.
The head of the Russian branch of Amnesty, Sergei Nikitin, told RIA Novosti the group had been renting the premises for 20 years and had paid for the current month.
The note left by the authorities said that the office was the property of the Russian state, as is the case with many buildings in Moscow.
Kremlin spokesman Dmitry Peskov told journalists he did not know anything about the closure of the office.
Amnesty has previously come under pressure from the Russian authorities.
In 2013, prosecutors searched its Moscow office and questioned Nikitin as part of a crackdown on non-governmental organisations that take an independent position from the authorities.