Vladimir Putin has overseen annual exercises by Russia's strategic nuclear forces at a time of heightened tensions with the West over his eight-month-long war in Ukraine.

Ballistic and cruise missiles were launched from the Arctic to Russia's Far East, the Kremlin said.

The US was told about the drill under the terms of the New Start arms treaty.

The launches took place as Russia makes unsubstantiated claims that Ukraine was plotting to use a "dirty bomb".

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 last Russian nuclear drill took place five days before it invaded Ukraine.

Ahead of the latest exercise, military officials in Washington pointed out that, in notifying the US, the Russians were complying with arms control obligations.

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.

Moscow has sent troops into the key southern city of Kherson to help defend it. Russia took Kherson in the early days of the war, but recently it has come under pressure as Ukrainian troops advance.

Defence Minister Sergei Shoigu was seen on Russian TV saying that the aim of the drill was for military command and control to practise carrying out "a massive nuclear strike by the strategic nuclear forces in retaliation for the enemy's nuclear strike".

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