Satellite photos raise concerns of Russian military build-up near Ukraine
(CNN) Once more, tensions are rising in Ukraine.
Reports that the Russians are moving military hardware some 250 kilometers from the border have raised eyebrows in Washington.
And Ukrainian forces have deployed combat drones along the battle lines that separate them from pro-Russian separatists in the Donbas region.
The front lines of the conflict a standoff stretching hundreds of miles from northern Ukraine to the Sea of Azov have barely moved in five years.
On Monday, US Defense Department spokesman Admiral John Kirby said the Pentagon was "aware of public reports of unusual Russian military activity near Ukraine."
Satellite imagery has shown Russian hardware including self-propelled guns, battle tanks and infantry fighting vehicles on the move at a training ground roughly 186 miles (300km) from the border. Ukraine's Defense Ministry said Monday it had recorded no "additional transfer of Russian units, weapons and military equipment to the state border of Ukraine."
On Tuesday, the Defense Ministry said an estimated 90,000 Russian troops were located "near the border and in the temporarily occupied territories" as well as in the Black Sea.
Ukraine's Defense Ministry added that Russia had established a practice of "transferring and accumulating military units for the purpose of maintaining tension in the region and political pressure on neighboring countries."
Kirby said the US was watching closely: "I can't speak for Russian intentions, but we are certainly monitoring the region closely, as we always do. Any escalatory or aggressive actions would be of great concern to the United Sates."
On Tuesday, Kremlin spokesman Dmitry Peskov told reporters: "The movement of our military equipment or army units across the territory of the Russian Federation is exclusively our business. Russia has never threatened anyone, is not threatening, and does not pose a danger to anyone," he insisted.
Observers say Russia's actions are worth keeping a close eye on.
"At the moment it is a developing situation. It's not 'nothing happening' and it doesn't mean that there will be an offensive op tomorrow," says Michael Kofman, a fellow at the Wilson Center who researches Russia's military.