Moscow said on Wednesday it would react in kind to United States' widening of sanctions imposed on Russia over the crisis in Ukraine, criticising the move as straining relations and posing risks for international stability.

The US Federal Register said on Wednesday Washington was adding 29 people to the sanctions list to tighten restrictions previously imposed on Russia.

Kremlin spokesman Dmitry Peskov said Russia's response would be reciprocal.

The Russian Foreign Ministry said that adding more sanctions on Moscow was illegitimate and added to a series of hostile actions taken by the United States against Russia.

It said the "reckless" US policy was "fraught with serious costs for international stability".

"The United States should have no illusions that it could continue this course without negative consequences for themselves," the ministry said.

"Response measures, not necessarily mirror ones, will follow from our side."

The new US sanctions cover people and entities linked to those already sanctioned, including Gennady Timchenko, a prominent Russian gas trader, Russia's top oil producer Rosneft and firearms maker Kalashnikov Concern.

Some of the entities are based in Cyprus, Finland, Romania, Switzerland and Britain.

They also target ferry operator and ports in Crimea, a Black Sea peninsula annexed by Russia from Ukraine last year, in a move that took relations between Moscow and the West to their lowest point since the Cold War.

Kiev and the West accuse Moscow of driving a pro-Russian separatist rebellion in east Ukraine, which started shortly after the Crimea annexation. Russia denies this.