The United States has imposed fresh sanctions on Russia relating to Ukraine, targeting six individuals and eight organisations, according to a statement from the US Treasury.

The move targets those who played a role in Russian attacks on Ukrainian ships in the Black Sea's Kerch Strait, Russia's 2014 annexation of Crimea, and its backing of illegitimate separatist government elections in eastern Ukraine, the statement said.

"The United States and our transatlantic partners will not allow Russia's continued aggression against Ukraine to go unchecked," Treasury Secretary Steven Mnuchin said.

"This joint initiative with our partners in the European Union and Canada reinforces our shared commitment to impose targeted and meaningful sanctions in response to the Kremlin’s attempts to disregard international norms and undermine Ukraine's sovereignty and territorial integrity," he added.

Among the sanctioned individuals were four Russian officials who were involved in the Kerch Strait attack off the coast of Crimea, the US Treasury said.

Six Russian defense firms with operations in Crimea were targeted for misappropriating Ukrainian state assets to provide services to the Russian military during the annexation, it said.