* VW's premium brand Audi sees sales drop due to WLTP
* Audi Sept global sales fall 22 pct, Europe down 55.5 pct
* VW brand says biggest selling cars now conform to new rules (Recasts with Audi)
FRANKFURT, Oct 5 (Reuters) - Volkswagen's premium brand Audi on Friday said it expected sales in Europe to fluctuate in the coming months after a 55.5 percent slump in September sales due to supply bottlenecks caused by stricter anti-pollution rules.
Last month VW Group's sales fell by half in Europe's five biggest markets, according to analysts at Citi, after several top selling models failed to conform to new the Worldwide Harmonised Light Vehicle Test (WLTP) rules.
Audi's monthly sales were down by 69.4 percent in Germany, while China deliveries increased 12.5 percent and sales in North America rose 1.2 percent, the carmaker said.
"Following above-average sales results in Europe over the past two months due to the sell-off of models in stock, the increasingly empty stores and the restrictions in the sales portfolio had an adverse effect on deliveries in September," Audi said.
Some of the supply bottlenecks that have slowed sales of VW's namesake brand, however, are now easing, VW said.
"Currently we have WLTP certification for volume sellers for all of our 14 models," it said in a statement.
"Further vehicle variants will gain their product release shortly," VW said, adding that by year-end it would be able to offer close to all models to customers. (Reporting by Edward Taylor; editing by Jason Neely and Maria Sheahan)