The warning by European Council President Charles Michel comes as last-ditch diplomatic efforts are under way to prevent, what Western powers say, the imminent Russian invasion of Ukraine.
European Council has warned western allies can't keep offering an olive branch while Russia continues to dial up tensions along the Ukrainian border.
"The big question remains: does the Kremlin want dialogue?" European Council President Charles Michel asked at the Munich Security Conference on Sunday.
"We cannot forever offer an olive branch while Russia conducts missile tests and continues to amass troops," he added.
His statement came as last-ditch diplomatic efforts were under way to prevent what Western powers warn could be the imminent Russian invasion of Ukraine and catastrophic European war.
French President Emmanuel Macron was to call his Russian counterpart Vladimir Putin as ceasefire monitors and Ukrainian commanders reported intense shelling in eastern Ukraine.
Artillery, mortar attacks
Macron met Putin on February 7 and has since, along with fellow Western leaders like Germany's Chancellor Olaf Scholz, been urging his Russian counterpart to pull back from the brink of war.
Sunday's call, Macron's office said, represented "the last possible and necessary effort to avoid a major conflict in Ukraine".
"Every indication indicates that Russia is planning a full-fledged attack against Ukraine," NATO chief Jens Stoltenberg said, echoing US President Joe Biden, who believes the invasion is imminent.
Hundreds of artillery and mortar attacks were reported in recent days, in a conflict that has rumbled on for eight years and claimed more than 14,000 lives.
Russia, according to Western leaders, has more than 150,000 troops along with missile batteries and warships massed around Ukraine, poised to strike.
Some 30,000 of these troops are in Belarus, ostensibly for an exercise alongside Putin ally Alexander Lukashenko's forces, but also close to the Ukraine frontier and the road to the capital Kiev.