Lufthansa and Swiss Air will suspend flights to the Ukraine capital Kyiv from Monday amid growing fears of a Russian invasion.
The German airline Lufthansa said it would also stop flights to Odessa, a key port on the Black Sea.
“The safety of our passengers and crew members is our top priority at all times,” said Lufthansa.
UK Prime Minister Boris Johnson warned on Sunday that Russia is planning “the biggest war in Europe since 1945”.
Last week, the Dutch airline KLM said that it was suspending flights to Kyiv.
The Lufthansa suspension is expected to remain in place until the end of February.
Both Lufthansa and Swiss say they will continue to monitor the situation closely and that they are in close contact with national and international authorities.
Swiss added: “The safety of our passengers and crew members has top priority at all times… The affected customers will be informed accordingly.”
A spokesperson for Lufthansa said: “Affected guests will be informed and rebooked on alternative flight connections.”
The airline usually operates 74 flights to Ukraine every week under its Lufthansa banner or the other carriers it owns which include Austrian Airlines, Eurowings and Swiss.
Lufthansa said it would continue to fly to Lviv in Western Ukraine.
Mr Johnson told the BBC that evidence suggests that Russia intends to launch an invasion that will encircle Kyiv.
“All the signs are that the plan has already in some senses begun,” he said.
Ryanair and Wizz Air also operate flights to Ukraine and last week said they would continue to fly to the country. Ryanair is the largest airline which flies between Europe and Ukraine, followed by Wizz Air.
In a statement on Sunday, Wizz Air said it was monitoring the situation closely and reminded passengers to check their inboxes regularly for further information about booked flights.
A Wizz Air spokesperson said: “Currently, we have not made any changes to our schedule and all of our flights to/from Ukraine continue to operate as normal.”
Ryanair’s chief executive Michael O’Leary said last week: “It is important not to panic.
“Is it our duty and obligation to support the people of Ukraine as long as there is no war or missiles flying there.”
The UK’s Foreign Office has advised that British nationals “should leave while commercial options remain”.
“In the event of a military incursion, it is likely that commercial routes out of Ukraine will be severely disrupted and roads across Ukraine could be closed,” it said.
Last week, the Ukrainian government pledged to keep the country’s airspace open. It said it was ready to assume financial obligations for flight safety amid concerns of rising insurance costs for airlines to keep flying into the region.
In July 2014, Malaysia Airlines flight MH17 was shot down while flying near eastern Ukraine’s conflict zone. All 298 passengers and crew on board the flight between Amsterdam and Kuala Lumpur were killed. The victims included 80 children.
An investigation by the Dutch Safety Board found that the plane crashed after being hit by a Russian-made Buk missile.BBC