Crypto exchange OKCoin has suspended the trading of two citycoins, MiamiCoin and NYCCoin, as of March 16, citing limited liquidity as the reason for the decision.

“Limited liquidity for these coins on our platform has created the possibility of price manipulation and fraudulent activity,” OKCoin wrote in a blog post. “While none of these risks have occurred, we wanted to get ahead of any possible misconduct.”

The exchange will resume the trading of those coins once the “unexpected” low liquidity is solved. Until then, holders can continue to keep their coins on the exchange or move them to a decentralized platform.

OKCoin, a globally licensed exchange headquartered in San Francisco, was the only centralized exchange that offered citycoins, according to the blog post.

Both MiamiCoin and NYCCoin are developed by CityCoins, which enables citizens a way to generate crypto-based revenue for themselves and the cities where they live.

Miami Mayor Francis Suarez was a particularly strong proponent of MiamiCoin in its early days, touting the possibility to generate a “bitcoin yield” for its citizens from its staking.

OKCoin didn’t immediately respond to a request for comment from CoinDesk.

Bloomberg previously reported on the news.