National Airlines flights from Long Island MacArthur Airport to Puerto Rico can’t start until at least three to six months after the airline acquires the plane it needs for the new service, the company said Thursday.

Florida-based National said it can no longer commit to the service until it obtains the aircraft for its six planned weekly round-trip flights.

“Sources saying National ‘won’t commit’ or is ‘pulling out’ are simply untrue. The fact is, National cannot commit because of this process — it’s not a decision in their control,” the airline said in a statement.

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The airline said it is working to get refunds to passengers who bought tickets, but would not say how many had been purchased.

National said Monday it was delaying its planned June 1 launch at MacArthur, but hoped to start flights later this year.

National’s name and logo has been removed from the MacArthur’s website.

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The Town of Islip, which owns and operates the airport, did not answer questions about the delayed launch or the airline’s contract.

A town spokeswoman said in a statement that Islip “remains very enthusiastic in welcoming National Airlines to our airport family.”

The airline said Thursday the delay “is completely due to a lack of availability of aircraft,” and that because of the lengthy process of acquiring and getting permits for an airplane, which can take six months, it cannot commit to serving MacArthur any sooner.

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“National has promised the Town of Islip to communicate openly with them to keep them apprised of any progress,” the airline said.

MacArthur, which has lost more than half its flights and almost half its passengers since 2007, has for years courted airlines to enhance its service. PenAir and Allegiant Air served the airport for less than a year after they started in 2013, and several promising leads — including rumors of flights from JetBlue and Air Canada — never panned out. The airport also ran a deficit of almost $7.5 million between 2010 and 2014.

But early this year, Gov. Andrew M. Cuomo announced $6 million in funding to help build a federal Customs facility to attract international flights there. The town also secured funding from Suffolk County and the state Regional Economic Development Council for the proposed $10 million facility.

National’s February announcement that it would start flying to San Juan and Aguadilla was welcome news, and it was followed by Elite Airways, which is scheduled to start flights at MacArthur on June 17.

National, which flies two Boeing 757s and began scheduled passenger service late last year, said it is now “identifying the appropriate aircraft” for MacArthur flights.

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The airline did not respond to questions asking why the company decided to serve MacArthur before securing the necessary aircraft.

Sources familiar with the situation said bookings for the flights to San Juan and Aguadilla were strong through summer, but sluggish overall and not close to what the airline hoped. National had planned to launch July 1, but moved that up a month because of demand, the airline said at the time.

National rejected the notion that bookings were anemic.