Experts say: How long does it take Russia to invade Ukraine

Russia continues to stockpile troops on the border with Ukraine, but no one still knows for sure what President Putin has in mind.

As many ask how imminent the threat of war is, analysts say Russia has a menu of options to attack at any moment, from air strikes to a ground invasion.

However, while deploying large quantities of military equipment in areas bordering Ukraine, not all the personnel needed for a ground operation are ready.

Troops can be deployed in less than 72 hours, as they have to be sent from their bases only by plane or train.

Russia has also deployed a "substantial formation" in Belarus that is moving west, including troops, logistics and communications resources, as well as military equipment.

Intelligence services say Russia is not yet in the lineup to attack. If attacked, Intelligence analysts predict that Putin may choose to invade through the Donbas, where there are many pro-Russian residents, and may intervene on the pretext that they need to be defended.

Some others suggest a narrow land corridor along the Sea of ??Azov. Another option is to invade the country extensively with air intervention, but this would come at a cost to Russia, as the West would impose tough sanctions.

Russia has deployed more than 106,000 ground personnel near Ukraine's borders and has 21,000 air and naval personnel at its disposal. It supports more than 35,000 rebels in eastern Ukraine and has about 3,000 of its military personnel in the territory.