PARIS (Reuters) -Airbus is struggling to increase output of its A350 jetliner as it faces ongoing delays in the arrival of fuselage parts from Spirit AeroSystems ( SPR ), industry sources said.

The delays have cast doubt on Airbus' ability to increase production above current rates of around six jets a month for at least the rest of this year, though it still hopes to reach its published target of 12 a month during 2028, they added.

A spokesperson for Airbus declined comment but referred back to comments given with its nine-month results in October, when Airbus upheld the 2028 target but said it was "actively managing specific supply chain challenges" that may affect 2025 output.

Spirit AeroSystems ( SPR ) declined comment.

Reuters reported in October that supplies to Airbus of key parts including a fuselage section from a Spirit plant at Kinston, North Carolina, were running behind schedule and Airbus later confirmed concerns over the pace of the ramp-up in 2025.

Now, it looks increasingly doubtful whether any significant increase in output of the long-haul A350 model will be possible at all in 2025 and possibly part of 2026, the sources said.

Spirit mainly supplies Boeing, which is in the process of buying back its former subsidiary, with Airbus taking control of the Kinston plant and a Belfast facility that supplies its A220.

Airbus halved A350 output to five a month during the pandemic and partially restored it to six a month in 2023, since when it has struggled to stay above that level, sources said.

In January this year, Airbus delivered two A350s.

The European group announces annual results on Thursday.