NATO Secretary-General Jens Stoltenberg called on Russia to be "transparent" about its military activities amid what he called a "large and unusual concentration" of Russian forces close to Ukraine's borders in recent weeks.
The United States and several European members of the alliance have raised alarm bells over Russian military activities near Ukraine, where Kremlin-backed separatists control swaths of territory in an ongoing seven-year conflict that has claimed more than 13,200 lives since April 2014.
"Any further provocation or aggressive actions by Russia would be of serious concern," Stoltenberg told a joint news conference with Ukrainian Foreign Minister Dmytro Kuleba in Brussels on November 15.
While in Brussels, Kuleba also met with French and German foreign ministers Jean-Yves Le Drian and Heiko Maas, who also warned Russia against harming Ukraine's territorial integrity.
"Any new attempt to undermine Ukraine’s territorial integrity would have serious consequences," Le Drian and Maas said in a joint statement after the talks, reaffirming that "Germany and France are steadfast in their unwavering support for the independence, sovereignty and territorial integrity of Ukraine" and urging Russia to "adopt a posture of restraint."
In London, a spokesman for Prime Minister Boris Johnson said on November 15 that Britain, too, remains "unwavering" in its support for Ukraine's territorial integrity.
"We are seeing a concerning situation at that border. We remain in unwavering support for Ukraine's territorial integrity and will continue to support them in the face of Russian hostility," the spokesman told reporters.
Meanwhile, U.S. Secretary of State Antony Blinken discussed "reports of concerning Russian military activity in and near Ukraine" with his French counterpart, according to the State Department.
Spokesman Ned Price said in a statement on November 14 that Blinken and French Foreign Minister Jean-Yves Le Drian also addressed their countries' "ironclad commitment to Ukraine's sovereignty and territorial integrity."
Last week, Blinken warned Russia against making another "serious mistake" on Ukraine as Washington sought information about an alleged Russian troop movement near the border that the Pentagon called "unusual in its size and scope."
Russian President Vladimir Putin has dismissed Western suggestions that Moscow might be considering offensive military action and accused Washington of aggressive moves in the Black Sea, where Ukraine and the United States have held major military drills in recent months.
Stoltenberg said on November 15 such exercises in the Black Sea region are "defensive and transparent."
On November 15, Putin signed a decree allowing goods produced in eastern Ukraine to be sold more easily in Russia.