(Recasts to say closure not caused by strike, adds Petrobras statement)
RIO DE JANEIRO, July 24 (Reuters) - An output cut at an offshore oil and gas platform owned and operated by Brazil's state-led oil company Petroleo Brasileiro SA was not caused by a 24-hour strike, a union involved in the action said late Friday.
The output cut on the P-15 platform happened on July 20, four days before the strike, after Petrobras, as the company is known, began adjustments to its gas compression system's turbo and motor compressors, Marcos Breda, communications director for SindepetroNF, a union representing platform workers, said.
SindipetroNF said earlier on Friday that the shutdown happened as a result of its members laying down tools starting at midnight Thursday.
It was not immediately clear why the union said that the strike was responsible for the platform shutdown.
Petrobras confirmed that the platform had been shut for repairs four days before the strike began.
According to FUP, a union federation to which SindipetroNF belongs, union workers struck at 19 offshore platforms in the Campos and Santos Basins. Production was not affected by the strike.
In May, the P-15, a semi-submersible vessel, produced 2,479 barrels per day of petroleum and 458,440 cubic meters of natural gas a day from the Marimbá and Pirauna fields, both 100 percent owned by Petrobras.
In May, output from the P-15 was about one-tenth of 1 percent of Petrobras' total Brazilian output of 2.61 million barrels of oil and equivalent natural gas a day. (Reporting by Marta Nogueira and Jeb Blount' Editing by G Crosse, Matthew Lewis and Andrew Hay)