US Secretary of State John Kerry met Wednesday with leading Russian human rights activists amid concerns about a crackdown by Russian authorities on pro-democracy movements and global civil society groups.

"Everybody has great respect for your efforts," Kerry said at the start of the meeting in the residence of US ambassador Michael McFaul.

Among the activists was 86-year-old Lyudmila Alekseyeva, head of Russia's flagship human rights organisation, the Moscow Helsinki Group.

She was joined by Ivan Blokov from Greenpeace Russia, activist Alexander Cherkasov from Memorial, one of the country's most prominent rights groups, human rights lawyer Pavel Chikov from the Agora Association and Tatyana Lokshina, deputy director of Human Rights Watch in Russia.

Russian authorities have in recent weeks begun questioning non-governmental organisations (NGOs) and searching their premises after adopting a controversial law requiring activist groups to declare themselves "foreign agents" if their funding comes from abroad.

The main US developmental agency USAID was abruptly expelled from Russia last year, as President Vladimir Putin accused US-funded groups of seeking to foment opposition to his rule.

Kerry met for more than five hours with Putin and Foreign Minister Sergei Lavrov on Tuesday for talks that focused on Syria and joint counter-terrorism efforts following the Boston bombings blamed on two brothers of Chechen descent.

Kerry told reporters he had also discussed the crackdown on NGOs and a controversial law banning US nationals from adopting Russian children.

But in an apparent bid to soothe months of tensions with Moscow, he suggested such disputes should not cloud ties, arguing that while they were important the two countries should not "get lost in some of these other issues."

"The key is not to let them become so personalised or so much an impediment to the larger goal and to the broader agenda and to our larger interests," he told reporters.