AS many as 40,000 Russian troops are massing on the country's border with Ukraine – prompting fears of a new military invasion.

The Pentagon has identified eight staging areas dotted along the border, suggesting Russian strongman Vladimir Putin is preparing for new incursions.

Among the units deployed to the area are armoured vehicles, tanks and fighter jets.

Navy Captain Danny Hernandez told the Washington Free Beacon that the exercises were being closely monitored.

He said: "We are extremely concerned about the increasing tensions near the administrative boundary between Crimea and the rest of Ukraine.

"We urge both sides to avoid provocative steps or rhetoric that could escalate the situation."

Officials told the publication similar movements were seen before Vladimir Putin carried out his deceptive annexation of the Crimea.

Such manoeuvres have reduced the "warning time" available to the US if he decides to launch another attack.

In June it was reported Russia was constructing an army base near the border which it considers to be a new front line with NATO.

A Reuters reporter who visited the Russian town of Klintsy, about 30 miles from Ukraine, saw a makeshift army camp, large numbers of newly-arrived servicemen and military vehicles.