The US has unveiled sanctions against six of Crimea’s breakaway leaders, including the official who signed a deal with Moscow to split the peninsula from Ukraine.

US officials have been warning for days that more sanctions against individuals and companies were in the works, as it calls on Moscow to de-escalate tensions and withdraw Russian troops from Ukraine’s eastern border in the worst East-West standoff since the Cold War.

A first wave of US sanctions unveiled in March notably blacklisted officials and business people close to Russian President Vladimir Putin to protest Moscow’s takeover of Crimea.

The new Treasury sanctions targeted the former vice speaker of Ukraine’s parliament, Sergei Tsekov, who helped pave the way towards the March referendum in Crimea that led to its annexation by Russia and was branded “illegal” by the West.

Tsekov now serves as Crimea’s representative in the Russian parliament.

The US Treasury also blacklisted Chernomorneftegaz, a gas company whose assets were seized by the Crimean parliament and are now managed by Moscow.

“Crimea is occupied territory. We will continue to impose costs on those involved in ongoing violations of Ukraine’s sovereignty and territorial integrity,” Under Secretary for Terrorism and Financial Intelligence David Cohen said.

The seven individuals targeted by the US have already been placed on EU sanctions lists.

News of the fresh American sanctions came as it was announced that four-way talks between the US, EU, Ukraine and Russia on the crisis would be held in Geneva on April 17.

US President Barack Obama told German Chancellor Angela Merkel on Thursday that the United States and its allies should prepare new sanctions against Russia if it escalates the crisis over Ukraine.