(CNN)The entire 30-member NATO alliance was united in its concern about the massive buildup of Russian forces near Crimea and along Ukraine's borders, US Secretary of State Antony Blinken said in Brussels, Belgium, on Wednesday.
"What was striking today was every single ally expressed the same concerns," said Blinken, speaking alongside US Defense Secretary Lloyd Austin and NATO Secretary-General Jens Stoltenberg.
Ukraine estimates that Russia has amassed as many as 50,000 troops in the region, while the current US assessment is that the Russian military has moved more than 40 battalion tactical groups into the border area, which could total up 40,000 troops. It is the largest buildup of Russian troops near Ukraine since 2014, when Russian forces invaded the country and occupied the Crimean Peninsula.
"It is a part of a broader pattern of Russian aggressive action, which raises very serious concerns," said Stoltenberg. "Allies fully support Ukraine's sovereignty and territorial integrity and we call on Russia to de-escalate immediately, stop its pattern of aggressive provocations and respect its international commitments."
On Tuesday, Gen. Tod Wolters, head of the US European Command, told the Senate Armed Services Committee the latest intelligence showed that a "very sizable" Russian ground force as well as "notable" increased air and naval forces had moved into the Ukraine border region and Crimea. "It is of the size and scale and scope that is of great concern, and it mirrors the size and scope and scale of the infiltration of forces that occurred back in 2014."
In addition, Russia has moved SA-22 air defense missile units into the region, according to a US official tracking Russian movements. That system is designed to protect Russian troops and critical military and civilian targets against air attack.
"We call upon Russia to cease their provocations and to be more transparent about this recent activity," said Austin, noting that the US has provided Ukraine with nonlethal materials, weapons and trainers, and that he expects that to continue.
The stark warning about Russia's growing military presence near its southwestern neighbor comes a day after President Joe Biden spoke with Russian President Vladimir Putin. Biden voiced US concerns about Russian forces, per a statement from the White House.
Pentagon officials say the current intelligence does not indicate that this land force is prepared for offensive operations in the next few days, because there is no evidence of the logistics, spare parts, fuel and medical capability that would need to be pre-positioned. But the concern remains that there are also no indicators of Russia reducing its forces or signaling a de-escalation. And events on the ground can change quickly, officials caution, noting that the intelligence assessments typically project out for only a few days at a time.
US reconnaissance aircraft are continuing to fly over the Black Sea to gather intelligence about Russian moves. The US assesses the Russians are likely to begin their own maritime war games in the area in the coming days.
The US Navy filed initial diplomatic paperwork with Turkey for permission to send two warships into the Black Sea in the coming days but has decided not to send the ships into the sensitive region, according to a defense official with direct knowledge. The destroyers are being kept out of the Black Sea for now, as the move is seen as too escalatory, US officials say. Instead, the ships will remain in the nearby Aegean Sea area, ready to respond if needed.
"We will remain vigilant," one official says.
Russia's deputy foreign minister, Sergey Ryabkov, warned the United States on Tuesday that it is better for the US Navy to stay away from the Russian Federation and Crimea, stating that the risks of incidents are very high, according to state news agency RIA.
The United States "must understand that the risks of certain incidents are very high. We have already observed something similar in a completely different water area this year. We warn the United States that it is better for them to stay away from Crimea, from our Black Sea coast. For their own good," Ryabkov told reporters.
Ukrainian President Volodymyr Zelensky told CNN's Matthew Chance that the US is a "good friend" of Ukraine, but that Biden "must do more," to deter Russia and help bring this conflict to an end.
