Russian authorities searched the Moscow offices of New-York based Human Rights Watch on Wednesday as they stepped up raids against pro-democracy groups despite growing concern from top European states.
Germany said the inspections risked affecting the two allies' relations while France sought an explanation from the Russian embassy about a check into the activities of its Alliance Francaise cultural outreach organisation.
HRW's Europe and Central Asia department head Rachel Denber said three representatives from the prosecutor's office and a tax official had undertaken what they called "an unplanned inspection" of the Moscow office.
She said the Moscow headquarters of the Civic Assistance refugees centre and of the Transparency International corruption watchdog had been raided in a similar manner.
"This is part of a massive, unprecedented wave of inspections of NGOs (non-governmental organisations) in Russia that is intensifying pressure on civil society in the wake of the adoption of a number restrictive laws last year," Denber said by e-mail.
"The scale of these inspections serves to reinforce the menacing atmosphere for civil society created by the adoption of last year's laws."
The raids followed President Vladimir Putin's signature of a law that labelled Russian political organisations with Western funding as "foreign agents" that required more rigorous checks.
Putin blamed the US State Department for funding the protests that rose against his return to the presidency last winter and moved quickly against the NGOs once confirmed to power in May.
Russian officials have not linked the probes to the foreign agent law directly and the action appears part of an in-depth examination of activities of non-governmental organisations that bother the state.
The authorities began their action last week by moving in against Memorial -- one of the country's most respected rights organisations whose vast catalogue of Stalin-era repressions is accessed by scholars around the world.
The Moscow office of London-based Amnesty International was searched on Monday while the Alliance Francaise office was inspected on Tuesday in the Volga city of Samara.
Groups such as Memorial have refused to change their registration to that of a "foreign agent" because they argued the legislation equated them with spies.
The raids have already raised eyebrows in Europe and threatened to further complicate ex-KGB agent Putin's uneasy relations with the West.
EU foreign policy chief Catherine Ashton on Tuesday called the inspections and searches "worrisome since they seem to be aimed at further undermining civil society activities in the country."
Germany also expressed its "concern" to the number two envoy of the Russian embassy in Berlin over an inspection of the offices of Konrad Adenauer Foundation (KAS) -- a political think tank with ties to Chancellor Angela Merkel's Christian Democratic Union.
A spokesman for Merkel warned Wednesday that "any action that interferes with or criminalises (the NGO's) main activities will degrade the relationship" between Russia and Germany.
He said Moscow's move may be discussed during a meeting between Merkel and Putin in Hannover next month while France asked the Russian embassy for an "explanation".
Activists estimate that at least 100 organisations have been inspected already in Moscow and Saint Petersburg as well as other parts of Russia.
They complain that the checks effectively paralyse their activities because staff are forced to dig through old documents and compile huge stacks of material for the myriad of Russian agencies with which they have to register.
One rights group posted a photograph on Twitter on Tuesday showing a pile of documents requested by the authorities that came out to more than a metre (three feet) in height.
Wednesday's inspections included a written request for more information from Agora -- a legal defence group based in the central Russian city of Kazan -- and a demand for the veteran rights advocate Lev Ponomaryov to appear for questioning.
Agora said the documents sought by the authorities included all the available information on its foreign funding for the past two years.