Ukraine on Sunday vowed to keep its airspace open to international travel despite Western warnings that Russian troops conducting drills near its borders could invade at any point.
The Dutch carrier KLM on Saturday became the first major airline to indefinitely suspend flights to the former Soviet republic because of the rising risks.
Ukraine's budget airline SkyUp said on Sunday that its flight from Portugal to Kyiv was forced to land in Moldova because the plane's Irish leasing company had revoked permission for it to cross into Ukraine.
SkyUP added that European leasing companies were demanding that Ukrainian airlines return their planes to EU airspace within 48 hours.
Ukraine's infrastructure ministry responded by holding an emergency meeting aimed at maintaining foreign travel and keeping the country from becoming more isolated in the heat of the crisis.
"The airspace over Ukraine remains open and the state is working on preempting risks for airlines," the ministry said after the meeting.
Industry analysts believe other international airlines may soon also ban flights into Ukraine because of the growing cost to travel insurers.
The travel industry is still haunted by the memory of Malaysia Airlines flight MH17 being shot down while flying near eastern Ukraine's conflict zone in July 2014.
All 298 passengers aboard the Amsterdam-Kuala Lumpur flight died.
Ukraine's infrastructure ministry acknowledged that "some carriers are facing difficulties linked to fluctuations on the insurance market."
"For its part, the state is prepared to support airlines and provide them with additional financial guarantees in order to support the market," it said.
The worries about air travel come with a growing number of Western governments winding down their diplomatic missions in Kyiv and advising citizens to get out of Ukraine as soon as they can.
The U.S. State Department on Saturday ordered all non-emergency embassy staff out of Ukraine.
Russia cited fears of "possible provocations from the Kyiv regime" as it also began pulling out some embassy staff.
The drawdown has touched the staff of the Organization for Security and Co-operation (OSCE) monitoring mission in Ukraine.
The OSCE has served as the world's eyes and ears for the eight-year conflict across Ukraine's Russian-backed separatist east that has claimed more than 14,000 lives.
But images on social media showed convoys of its white SUVs leaving various parts of the conflict zone because of the staff's need to comply with their respective governments' travel advisories.
Russian foreign ministry spokeswoman Maria Zakharova said on Sunday that the mission's partial withdrawal caused "serious concern" in Moscow because the move further ramped up tensions.
The Ukrainian government has been trying to preempt the flood of foreigners leaving the country by calling for calm and criticizing U.S. warnings of war breaking out "any day."
Ukrainian President Volodymyr Zelensky said on Saturday that "all this information is only provoking panic and not helping us."
Zelensky's office stressed on Sunday that "the sky over Ukraine remains open."
"The European Union Aviation Safety Agency also has not issued any recommendations to limit flights over Ukrainian airspace," Zelensky's deputy chief of staff Kyrylo Tymoshenko wrote on Facebook.
"Ukraine is ready to support airlines," he added. "The government will adopt the required measures soon."