Russian President Vladimir Putin on Thursday announced a military operation in Ukraine and vowed retaliation against those who interfere with it, AFP reported.

He urged Ukrainian military forces to lay down their arms, and said that all personnel who do so will be able to freely leave the combat zone and return to their families.

This comes a day after he said that Russia was looking for “diplomatic solutions” to resolve the tensions with Ukraine, but that its interests are non-negotiable.

Early on Thursday morning, explosions could be heard during a CNN report from Ukraine’s capital of Kyiv.

Putin said that Russia was left with no choice but to defend itself against what he claimed were threats emanating from Ukraine, Reuters reported. He claimed that Russia was seeking to de-militarise and “de-Nazify” Ukraine.

“All responsibility for bloodshed will be on the conscience of the ruling regime in Ukraine,” the Russian president said. “No one should have any doubt that a direct attack on our country will lead to defeat and terrible consequences for any potential aggressor.”

Russia’s ambassador to the United Nations Vasily Nebenzya claimed that the country’s operation was aimed at protecting people in the separatist regions of Ukraine “who for eight years have been cowering from Ukraine’s shelling”, CNN reported.

Ukrainian President Volodymyr Zelenskyy rejected Moscow’s allegation that his country posed a challenge to Russia and said that an invasion could lead to the loss of thousands of lives.

“The people of Ukraine and the government of Ukraine want peace,” he said in an appeal to the people of Russia, according to AP. “But if we come under attack, if we face an attempt to take away our country, our freedom, our lives and lives of our children, we will defend ourselves. When you attack us, you will see our faces, not our backs.”

Zelenskyy claimed that he attempted to arrange a call with Putin late on Wednesday, but the Russian side did not respond.

Ukraine-Russia tensions

Since early this year, the country has amassed over 1 lakh troops at the Ukrainian border, leading to fears of an invasion.

The two countries have been engaged in a conflict since 2014 when Russia annexed Ukraine’s Crimean Peninsula and backed separatist rebellions in the country’s eastern regions of Donetsk and Luhansk.

On Monday, Putin had said he recognised the independence of separatists in Donetsk and Luhansk.