MOSCOW, July 17 (Reuters) - State-owned Russian agricultural bank Rosselkhozbank on Wednesday warned customers that its cards issued with China's UnionPay system would stop working outside Russia from July 19, creating a potential payment headache for clients.

UnionPay, along with domestic payment card system Mir, is one of few options left for Russians to make payments abroad after Russian banks were isolated from the global financial system over the conflict in Ukraine and Visa and Mastercard suspended their Russian operations.

With Mir payments adopted in only a handful of other countries, a narrowing of UnionPay options would further complicate matters for Russians making payments abroad.

"If you are outside Russia, we recommend that you withdraw cash from your UnionPay card before (July 19)," Rosselkhozbank said on Telegram.

Rosselkhozbank did not immediately respond to a request for comment on why it was suspending UnionPay operations.

The maximum daily withdrawal limit is 500,000 roubles ($5,688.28), Rosselkhozbank said.

Ballooning trade between Russia and China is being restrained by payment problems, with larger lenders deterred by the threat of secondary U.S. sanctions on Chinese banks that facilitate trade with Russia.

Moscow and Beijing have had to take complex steps to try to avoid payment delays, including a workaround using small, regional Chinese banks. ($1 = 87.9000 roubles) (Reporting by Elena Fabrichnaya Writing by Alexander Marrow Editing by David Goodman)