Vladimir Putin has given the order for his troops to invade Ukraine, with the Russian army now poised to strike. 

That's according to US intelligence, which has revealed about three-quarters of Russia's total forces have been deployed against Ukraine. 

An insider with knowledge of the unfolding crisis told US news outlets including CNN and CBS that the sheer number of troops now massed close to Ukraine indicates an attack could be imminent. 

According to CNN, 120 out of Russia's 160 Battalion Tactical Groups (BTGs) are now within 60km of Ukraine, a figure which represents 75 per cent of the country's principal combat units. 

The network also claims that there could be almost 200,000 Russian and separatist forces positioned in the area, with 35 of 50 known air defence battalions deployed against Ukraine. 

There are also around 500 fighter and fighter-bomber aircraft and 50 medium to heavy bombers within range of Ukraine. 

CBS also reports commanders have been ordered to proceed with an invasion, with specific plans being made as to how to manoeuvre troops on the battlefield. 

Emergency talks 'within hours' 

French President Emmanuel Macron and Vladimir Putin have agreed on "working intensively to enable a meeting of the Trilateral Contact Group to be held in the next few hours", the Élysée Palace has confirmed, with an objective to "obtain a commitment from all parties to a ceasefire on the line of contact". 

US President Joe Biden is expected to speak today alongside Macron following the latter's following phone calls with Putin and Ukrainian President Volodomyr Zelensky. 

Mystery symbols spark fears 

It comes amid growing concern over a recurring symbol appearing on Russian tanks massing at the border with Ukraine. 

Aric Toler, a reporter from Bellingcat, a Netherlands-based investigative journalism group, noted that some Russian vehicles but not others have been marked out with a white square and a "Z" over the top. 

Toric said his news organisation had "been monitoring this stuff non-stop for eight years and has no idea what they [the Zs] are, and hasn't seen it before. 

"So, assume the worst, I guess/fear." 

Some have referred to it as the "Zorro squad". 

The trend has only been observed in the past 24 hours as far as news.com.au can tell. 

Some have speculated that the ominous signs are a way to make sure Russians can tell their own vehicles apart from their enemies. 

This was a practice employed by the Allies in World War II to reduce the chance of soldiers firing on "friendly" forces. 

- by Alexis Carey, news.com.au