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Shares in firms controlled by Oleg Deripaska have plunged after the US imposed sanctions on seven Russian oligarchs and their companies on Friday.

Shares in the Russian aluminium giant Rusal nearly halved on the Hong Kong stock exchange on Monday.

EN+, the aluminium to hydropower firm controlled by Mr Deripaska, dived by 25% in London.

Russia's stock market tumbled on Monday in the wake of the sanctions.

They follow a diplomatic crisis sparked by the poisoning of former spy Sergei Skripal in Salisbury.

The measures affect the seven oligarchs, 12 companies they own or control, as well as 17 senior Russian government officials.

The Kremlin slammed the sanctions. "This is an outrageous business from the point of view of illegality, from the point of view of flouting all the norms, and of course careful analysis is needed here," said spokesman Dmitry Peskov.

The Russian government was "doing everything possible to minimise negative consequences" of the US measures, he added.

According to Washington, the individuals and companies were targeted for profiting from a Russian state engaged in "malign activities" around the world.

Other magnates hit by sanctions include Alexei Miller, director of state-owned energy giant Gazprom.

Rusal, which produces about 7% of the world's aluminium, said it regretted its inclusion on the new US sanctions list.

The company said the sanctions were likely to have a "materially adverse" impact on its business and finances.

"Rusal will probably have to be bailed out by Russian state banks," wrote analysts at TS Lombard.

Mr Deripaska may also be forced to sell his stake in Norilsk Nickel, losing a drawn-out battle with Vladimir Potanin for control of the metals giant, they added.

In Moscow the dollar-denominated RTS index ended 11.2% lower and the rouble-based MOEX Russian index shed 7.7%, while the rouble fell 3% against the US dollar.

Shares with Russian exposure listed elsewhere were also hit. Shares in Russian steelmaker Evraz were the biggest fallers on the FTSE 100 in London, closing 14.4% lower.

"The US list may not be the final list and it feels like there will be more sanctions, so investors do not know which, if any, stocks to hold," said John Meyer, mining analyst at SP Angel.

"US investors have to sell their interests in Rusal and En+ among others by 7 May."

Jasper Lawler, head of research at London Capital Group, added: "The sanctions make it almost impossible for these Russian firms and their billionaire owners to transact in US dollars, the main currency used in international trade and the standard denomination for commodities."

The US said it imposed the latest sanctions because of Russian activity in Ukraine, its support of President Bashar al-Assad in Syria's civil war and for subverting Western democracies.

It has also expelled dozens of Russian diplomats in response to the poisoning of a former Russian spy in the UK.

On Friday Russia's foreign ministry said there would be a "tough response" to the sanctions.