Norse Atlantic ASA will delay the debut of Norway-U.S. services after the Russian invasion of Ukraine resulted in surging fuel prices and uncertainty about demand.

The startup carrier, which had aimed to begin commercial operations in spring 2022, will now sell tickets in April and commence flights from Norway in June, according to a statement Tuesday. It also secured operating slots at London Gatwick airport at no cost but doesn’t immediately plan to start services.

Norse, founded by executives with ties to Norwegian Air Shuttle ASA, intends to start flying between Norway and destinations in the U.S. The airline then has plans to add European cities such as Paris and London, “as soon as the market situation allows.”

“The tragedy unfolding in Ukraine creates uncertainties within international air transport that we take seriously,” Bjorn Tore Larsen, founder and chief executive officer said in the statement. “A gradual approach where ramp-up is exclusively driven by demand will enable us to preserve our strong, debt-free balance sheet and cost base.”

The carrier said lease terms allow it to only pay for aircraft when they are in operation. 

Norse has begun training pilots and cabin crew for its initial routes, though their induction will be gradual to ensure the cost of paying crew happens immediately before the start of services.