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.

* The immediate call-up of 300,000 military reservists whohave previously served in the Russian army and have combatexperience or specialised military skills. Students orconscripts - young men serving mandatory 12-month terms in thearmed forces - will not be included. * The military is looking for reservists who have donespecific and specialised jobs in the army in the past, such astank drivers, sappers and snipers. However, the exact list ofspecialities it requires is classified as that would revealwhere Russia has personnel gaps. * Critics have said the wording of the mobilisation decreeand details of who will and will not be included looks to havebeen left deliberately vague to give the authorities a widedegree of latitude when implementing it. There is no mention ofthe 300,000 figure in the decree as published, which came froman interview that Sergei Shoigu, the defence minister, gave tostate TV. The Kremlin said that part of the decree, which itsaid made reference to up to 300,000 people being mobilised inphases, had deliberately not been published. It was not clearwhether other details had been deliberately withheld too. * The reservists' main task, according to Shoigu, will be toreinforce the front line in Ukraine, which is currently over1,000 km (621 miles) long. "Naturally what is behind this lineneeds to be reinforced, the territory needs to be controlled,"Shoigu told state television. * The reservists cannot physically be deployed to Ukraineimmediately as they will need to first undergo refresher or newtraining and be made familiar with the way Russia prosecuteswhat it calls its "special military operation". Western militaryanalysts forecast it will therefore be several months beforethey see action. * Professional soldiers known as 'kontraktniki' who arecurrently serving in the armed forces will have their contractsautomatically extended until the authorities decide to end theperiod of temporary mobilisation. In other words, it just becamemuch harder for serving professional soldiers to quit. * Only age grounds, valid health complaints verified by amedical-military commission, or those who have been sentenced tojail time by a court can be discharged from the army or reserveforce. People working in the defence industry can defer service. * A day earlier, the Russian parliament approved a bill totoughen punishments for crimes such as desertion, damage tomilitary property and insubordination if they are committedduring military mobilisation or combat situations. According toa copy of the legislation, seen by Reuters, voluntary surrenderwould become a crime for Russian military personnel punishableby 10 years in prison. * Reservists will be financially incentivised and be paidlike full-time serving professional soldiers who make much moremoney than the average Russian wage. That may make theproposition more attractive for some men in the provinces wherewages are traditionally lower than in big cities. * Western military analysts have queried whether Russia hasenough military equipment and hardware after its losses inUkraine, as well as enough experienced military trainers, toproperly prepare and deploy the reservists. Moscow says it does. * Western military analysts are divided on whether partialmobilisation is too little too late to alter the course of thewar in Moscow's favour. Most say they think it is too late, buta few say it could help Russia in some ways, though notimmediately and not conclusively. * The mobilisation announcement appears to have caused panicamong some potential reservists. One-way flights out of Russiawere selling out fast on Wednesday, according to ticket salesdata, and there were unverified media reports of some men beingturned back by Russian border guards. * Jailed opposition politician Alexei Navalny predicted onWednesday that many men would try to dodge the draft. * Activists from the Vesna (Spring) anti-war coalitioncalled for Russians to protest against the mobilisationannouncement as early as Wednesday evening in city and towncentres. Any such protests are likely to be broken up by theauthorities. Under Russian law only demonstrations sanctioned inadvance by the authorities are deemed legal. * "This (mobilisation) means that thousands of Russian men -our fathers, brothers and husbands - will be thrown into themeat grinder of war," Vesna said in a statement. "Now the warwill really come to every home and every family." * Small protests broke out in some Russian cities onWednesday.

(Reporting by Andrew Osborn; Editing by Mark Heinrich)

By Andrew Osborn