As Russian troops massed on Ukraine’s eastern border, the Pentagon announced Monday that it was putting 8,500 U.S. soldiers on high alert for potential deployment to help defend against a possible invasion. As a result, airlines looked to hike up their prices as people attempted to flee the country.

Newsweek examined the Tuesday versus Wednesday airfares of four large carriers that service Ukraine’s capital city of Kyiv: Swiss Air Lines, Lufthansa, Austrian Air, and the country’s flag carrier, Ukraine International Airlines (UIA).

All airfares were listed as economy class one-way tickets from Ukraine’s largest hub, Boryspil International Airport, to John F. Kennedy International Airport in New York City. The majority of these airfares allowed for at least one stopover or transfer in a number of different European cities.

The most dramatic price increase was from UIA, which showed a best Tuesday airfare of $29 and a Wednesday best $67. While UIA is often known for its low fares and cheaper options, this still represents a day-to-day price increase of 131 percent.

On the other end of the spectrum lies Swiss Air Lines. The flag carrier of Switzerland is rated as a four-star airline by the aviation review site Skytrax, and has prices to match.

For Tuesday, Swiss Air Lines showed a low price of $455, which increased to $499 on Wednesday, a 10 percent spike. The airline then drops airfare back down to $396 for Thursday, a 20 percent dip.

But the highest airfare seemed to be from Austria’s flag carrier, Austrian Air, another line often considered to be among the top in Europe. Austrian Air was offering $795 tickets out of Kyiv on Tuesday, which increased to $839 on Wednesday.

By Friday, the lowest airfare had dipped down to $669, dropping 15 percent in just three days.

Almost identical pricing was seen by Lufthansa, the flag carrier of Austria’s next-door neighbor, Germany. Getting on a Lufthansa flight out of Kyiv would set passengers back $790 on Tuesday, which increased to $834 on Wednesday.

However, Lufthansa, too, had lowered its price to $665 by Friday, another 15 percent decrease.

Lufthansa owns Austrian Airlines as well as a number of other subsidiaries, which may help explain the similar flow in pricing between the two airlines.

The price bumps come following a report that four European airlines would cease operations at Boryspil International Airport due to fears over the potential for violence in Ukraine.

This includes Lufthansa, Swiss Air Lines and Austrian Air. Also pulling their planes was the Dutch-based KLM.

These four airlines reportedly worked to shift around schedules and plane departures to minimize the amount of time that their flight crews spent in Ukraine.

Aviation lawyer Andriy Guck told Ukrainian news source The Kyiv Independent that it is fairly common “for airlines to be volatile to the situation and make sudden changes to their flight schedule if they sense some danger.”

Guck told the outlet that the airlines were simply trying to reduce their operational risks. However, he didn’t believe that all flights would have to be canceled at this point.

When reached for comment, a spokesperson for Swiss Air Lines told Newsweek that in general, the development of ticket pricing was related to offer and demand. They did not elaborate on the specifics of the situation in Ukraine.

Newsweek has also reached out to UIA, Lufthansa, and Austrian Air for comment.

Update (01/25/2022, 4 p.m. ET): This story has been updated with a comment from Swiss Air Lines.