Moscow/Kyiv – Putin oversaw the country’s annual nuclear drills on Wednesday in an exercise involving nuclear submarines, strategic bombers and ballistic missiles at a time when tensions are high over a it has made against Ukraine.
A "dirty bomb" is an explosive device mixed with radioactive material and the Russian allegations have been widely rejected by Western countries as false.
Kyiv warned the claims indicate Moscow itself could be preparing such an attack.
The US was told about the drill under the terms of the New Start arms treaty.
Washington said the notification lowered the risk of miscalculation at a time of "reckless" Russian nuclear rhetoric, while Western officials have expressed confidence in their ability to discern the difference between a Russian drill and preparations for a real nuclear strike.
Nato is also staging its own nuclear exercises, dubbed Steadfast Noon, in north-western Europe. The Western defensive alliance said training flights involving 14 countries were taking place until Sunday over Belgium, the UK and the North Sea.
Russia's exercises were being held against a backdrop of a flagging campaign in southern and eastern Ukraine.
Test launches of nuclear-capable intercontinental ballistic missiles from land and sea, and cruise missiles fired from the air by TU-95MS strategic bombers, had passed off successfully, Chief of Staff Valery Gerasimov added.
Putin later told a meeting of intelligence officials from ex-Soviet countries that the potential for conflict in the world remained high.
On the ground in Ukraine, the Russian defence ministry said its forces had repelled attempted Ukrainian advances in the south and the east.
Western officials have expressed fears that Moscow may be tempted to use a low-yield "tactical" nuclear weapon in Ukraine to try to force Kyiv to capitulate at a time when the Ukrainian pressure on the Russian forces around Kherson threatens a major defeat for Moscow.
U.S. President Joe Biden warned Russia on Tuesday that such a move would be an "incredibly serious mistake."
A day after Russia aired its "dirty bomb" allegations at the U.N. Security Council, the Russian Minister, Sergei Shoigu briefed his Chinese counterpart Wei Fenghe by video to convey Moscow's concern.
A close Putin ally, Shoigu held a similar video conference with his Indian counterpart, Rajnath Singh. Singh reportedly told Shoigu that nuclear weapons should not be used by any side.
Singh called for an early resolution to the conflict through diplomacy, a prospect which, for now, seems remote after eight months of war amid a successful Ukrainian counter offensive that has forced Russian troops to retreat.
-BBC/Reuters