DONETSK, Ukraine — The pro-Russia insurgency in eastern Ukraine decided today to go ahead with Sunday’s referendum on autonomy despite a call from Russian President Vladimir Putin to delay it.

While Putin’s call on Wednesday to postpone the vote was seen as part of an effort to step back from confrontation and negotiate a deal with the West, he fueled tensions again today by overseeing military exercises that Russian news agencies said simulated a massive retaliatory nuclear strike in response to an enemy attack.

Putin said the exercise involving Russia’s nuclear forces had been planned back in November, but it came as relations between Russia and the West have plunged to their lowest point since the Cold War.