Satellite photos show Russian troops deployed near Ukraine border

A close view of tanks artillery and tents in the Pogonov training area of Voronez, Russia.

US President Joe Biden predicted on Wednesday that Russian President Vladimir Putin's decision on whether Russia will move into Ukraine will depend "on which side of the bed he gets up on."

The Kremlin has massed some 100,000 troops near Ukraine's borders, a buildup that the West says is preparation for a war to prevent Ukraine from ever joining the NATO Western security alliance. Russia denies planning an invasion.

A closer view of tank artillery and support equipment from the deployed units in Yelnya which is 130km east of Russia-Belarus border.

Biden and his team have prepared a broad set of sanctions and other economic penalties to impose on Russia in the event of an invasion.

Visiting Kyiv in a show of support, US Secretary of State Antony Blinken said Russia could launch a new attack on Ukraine at "very short notice" but Washington would pursue diplomacy as long as it could, even though it was unsure what Moscow really wanted.

An overview of deployed units in Yelnya.

The Kremlin has said tension around Ukraine was increasing and it still awaited a written US response to its sweeping demands for security guarantees from the West.

Russia wants a halt to further NATO expansion and a withdrawal of alliance forces from central and eastern European nations that joined it after 1997.

Equipment deployed at Klimovo, in Bryansk Oblast which is 13 kilometres north of the Russia-Ukraine border at a storage facility in Russia.

On a visit to Kyiv to show support for Ukraine, US Secretary of State Binken said Ukrainians should prepare for difficult days.

He said Washington would keep providing defence assistance to Kyiv and renewed a promise of severe sanctions against Russia in the event of a new invasion.

A close view of armoured personnel carriers and trucks at Klimovo storage facility in Bryansk Oblast which is 13 kilometres north of the Russia-Ukraine border at a storage facility in Russia.

Blinken has promised "relentless diplomatic efforts to prevent renewed aggression and to promote dialogue and peace."

He said a Russian build-up of tens of thousands of troops near the Ukrainian border was taking place with no provocation and no reason.

Ukrainian foreign minister Dmytro Kuleba accused Russia of trying to sow panic in Ukraine. He said diplomacy offered the only way out, and it was an "indestructible principle" that no decisions about Ukraine could be taken without its involvement.

The new helicopters are a modernised version of an older KA-50 'Black Shark' type.

According to the Russian ministry of defence, the latest avionics and improved battle assault systems allow the helicopters to engage in combat at any time of the day and in any weather conditions.

The arrival of new 'Alligators' comes amid escalating tensions on the Ukrainian border where Russia massed tens of thousands of troops, raising fears of an invasion and prompting warnings from the West.

The Kremlin had said earlier that tension around Ukraine was increasing, pointing to weapons deliveries, military maneuvers and NATO aircraft flights, something it said Russia's international partners should pay take into account.

Kremlin spokesperson Dmitry Peskov said Moscow hoped to receive written answers to its proposals for sweeping security guarantees in the coming days.

Western countries say they fear Russia is preparing a pretext for a new assault on Ukraine, which it invaded in 2014.

Moscow however denies any plans for an attack, but has said it could take unspecified military action unless the West agrees to a list of demands, including banning Ukraine from ever joining NATO.

The US administration had approved $200 million in additional defensive security assistance to Ukraine in December.

Britain's military aid began arrived in Ukraine on January 18 including anti-tank weapons to help Kyiv defend itself from a potential invasion during a stand-off with Russia which has massed troops near the Ukrainian border.

Britain has previously warned Russia of severe consequences if it launched a new military assault on Ukraine, while offering financing to enhance Ukraine's naval capabilities.

Russia denies planning a new military offensive but has made several demands and said it could take unspecified military action unless the West agrees to them.