As Russian forces struggled to hold a key city in Ukraine’s south, the Kremlin raised the prospect of using nuclear weapons once more.

Former Russian President Dmitry Medvedev, who is now the deputy chairman of the country’s security council, said Moscow could strike an enemy using only conventional weapons, while Vladimir Putin’s defence minister said nuclear “readiness” was a priority.

The remarks on Saturday prompted Ukraine’s president, Volodymyr Zelenskiy, to warn that Moscow was a direct threat to the world during a video link appearance at Qatar’s Doha Forum.

“Russia is deliberating bragging about being able to destroy not just a specific country, but the entire planet with nuclear weapons,” Zelenskiy said.

Putin established the nuclear threat early in the war, warning that western intervention would result in “consequences you have never seen.”

According to Western officials, the threats may simply be an attempt to divert attention away from Putin’s forces’ failure to secure a swift occupation of the Ukrainian capital, Kyiv, and to make advances in other key areas of the country.

Markian Lubkivskyi, an adviser to Ukraine’s defence ministry, claimed on Saturday that Russia would soon lose control of the southern city of Kherson, the first major centre to fall to the Kremlin since the war began on February 24.

“I believe that the city will be fully under the control of Ukrainian armed forces today,” he said. We completed the operation in the Kyiv region in the last two days, so other armed forces are now focusing on the southern part of the country, attempting to liberate Kherson and other Ukrainian cities.”

Russia has approximately 6,000 nuclear warheads, making it the world’s largest stockpile of nuclear weapons. In an interview on Saturday, Medvedev stated that Russia’s nuclear doctrine does not necessitate the use of nuclear weapons by an adversary.

“The third is an attack on a critical infrastructure that will have paralysed our nuclear deterrent forces. And the fourth case is when an act of aggression is committed against Russia and its allies, which jeopardised the existence of the country itself, even without the use of nuclear weapons, that is, with the use of conventional weapons.”

Medvedev went on to say that there was a “determination to defend our country’s independence, sovereignty, not to give anyone even the slightest reason to doubt that we are ready to give a worthy response to any infringement on our country, on its independence.”

Sergei Shoigu, Russia’s defence minister, who had not been seen in 12 days before making a brief appearance on Friday and delivering an address to his generals on Saturday, also addressed the nuclear threat contained within Russia’s arsenal.

Shoigu stated in a video posted on social media by the Russian defence ministry that he discussed issues concerning the military budget and defence orders with the finance ministry.