Russia on Thursday branded US sanctions against Chechen strongman Ramzan Kadyrov "illegal and unfriendly" after Washington accused the key Kremlin ally of involvement in murder and torture.

On Wednesday, the US Treasury hit the Chechen leader with financial sanctions under the 2012 Magnitsky Act, accusing Kadyrov of personal involvement in repression, torture and extra-judicial killings.

"We consider these sanctions to be illegal, we consider them unfriendly, we disagree with them," President Vladimir Putin's spokesman Dmitry Peskov told journalists.

Asked whether Moscow will respond to the move, Peskov said: "With some certainty, we can assume that the principle of reciprocity will be observed."

He did not provide further details.

The Russian foreign ministry struck a similar note.

"This all looks very grotesque because it is not rooted in reality," foreign ministry spokeswoman Maria Zakharova said.

"These steps will lead to reciprocal measures," she added.

"It is sad that a number of groups in the United States still have an obvious desire to pursue the path of destroying bilateral ties."

Kadyrov, 41, is one of the most prominent Russian officials to be added to the sanctions under the Magnitsky Act.

A former rebel turned Putin loyalist, Kadyrov has his own militia army and rules with an iron grip the North Caucasus region that was the scene of two separatist wars.

Critics have accused him of amassing vast personal wealth and abusing his political post.

The new penalties, which also target other Russian officials, expose the difficulty of a rapprochement between Washington and Moscow expected by many since US President Donald Trump's election last year.

Relations between the two former Cold War adversaries hit a new low following a US investigation into accusations of Russian interference during the 2016 US presidential election and suspicion of a possible collusion between the Kremlin and Trump's campaign team.

Source: AFP