LONDON - President Vladimir Putin on Wednesday ordered Russia's first mobilisation since World War Two after suffering a major battlefield reversal in Ukraine, an attempt to turn the military tide in what he has cast as a defining East-West clash.

The mobilisation is, for now, being officially described as a partial one that will steadily draw in 300,000 reservists from across the world's largest country over a period of months, rather than a full call-up that would rely on what Russia's defence minister says is a vast reserve force of 25 million people.

Men and women aged from 18 to 60 years old can theoretically be called up as reservists according to Russian legislation, depending on their rank.

Western military analysts have long said that Russia is suffering serious manpower shortages on the Ukraine battlefield due to heavy losses, while Russian nationalists have for months been calling for some kind of mobilisation to inject new life into what they have described as a stuttering campaign.

Ukraine launched its own mobilisation programme two days before Russia's Feb. 24 invasion and soon afterwards announced martial law, which banned men aged 18-60 from leaving the country. It is currently on its fourth wave of mobilisation. The exact number of mobilised reservists in Ukraine is classified but official pronouncements suggest it is at least 400,000.

Here are the main elements of Russia's mobilisation plan, some of which is set out on the Kremlin website in a decree signed by Putin, and other parts of which have been fleshed out by Putin himself or his defence minister.

  - Reuters