Ukraine on Saturday urged its citizens to keep calm and avoid panicking in the face of mounting worries that Russia is preparing to invade its neighbor.

"At the moment, it is critically important to remain calm, to consolidate inside the country, to avoid destabilizing actions and those that sow panic," the Ukrainian Foreign Ministry said in a statement.

The appeal came a day after the United States and a host of European countries urged their citizens to leave Ukraine immediately because of the growing danger of a full-scale offensive by Russian forces encircling the former Soviet state.

Washington dramatically raised the stakes on Friday by warning that Russia could attack "any day now." The United Kingdom and the U.S. advised their nationals to leave Ukraine on Friday amid the possibility of a military operation by Russia.

Australia and New Zealand on Saturday became the latest countries to warn their citizens in Ukraine to leave immediately, as fears of a Russian invasion rise.

Some of the United States' media suggested the invasion could begin shortly after German Chancellor Olaf Scholz concludes talks with Russian President Vladimir Putin in Moscow on Tuesday.

Kyiv has been trying to tone down the warnings coming out of Washington throughout the crisis.

The Ukrainian government fears U.S. statements are hurting public morale and damaging the country's struggling economy by crimping business activity.

"The armed force of Ukraine is constantly monitoring the situation and are ready to rebuff any encroachment on its territorial integrity and sovereignty," the foreign ministry said.

"Ukrainian diplomats are in constant contact with all its key partners, swiftly receiving the information needed to prepare a well-timed response."

Russia says it has no plans to invade but wants the West to keep Ukraine and other former Soviet countries out of NATO. It also wants NATO to refrain from deploying weapons there and to roll back alliance forces from Eastern Europe – demands flatly rejected by the West.

Russia and Ukraine have been locked in a bitter conflict since 2014 when Ukraine’s Kremlin-friendly leader was driven from office by a popular uprising. Moscow responded by annexing Crimea and then backing a separatist insurgency in eastern Ukraine, where fighting has killed over 14,000 people.

A 2015 peace deal brokered by France and Germany helped halt large-scale battles, but regular skirmishes have continued, and efforts to reach a political settlement have stalled.